Posts Tagged ‘oligonucleotide’

DNA Replication

Larry H. Bernstein, MD, FCAP, Curator




Decades Old DNA Replication Models Called into Question


Decades Old DNA Replication Models Called into Question

A series of electron micrographs show the barrel-shaped helicase, which is the enzyme that separates the two DNA strands, along with other components of the replisome, including polymerase-epsilon (green).[Brookhaven National Laboratory]

  • It may be time to update biology texts to reflect newly published data from a collaborative team of scientists at Rockefeller University, Stony Brook University, and the U.S. Department of Energy’s Brookhaven National Laboratory. Using cutting-edge electron microscopy (EM) techniques, the investigators gathered the first ever images of the fully assembled replisome, providing new insight into the molecular mechanisms of replication.

    “Our finding goes against decades of textbook drawings of what people thought the replisome should look like,” remarked co-senior author Michael O’Donnell, Ph.D., professor and head of Rockefeller’s Laboratory of DNA Replication. “However, it’s a recurring theme in science that nature does not always turn out to work the way you thought it did.”

    “Our finding goes against decades of textbook drawings of what people thought the replisome should look like,” remarked co-senior author Michael O’Donnell, Ph.D., professor and head of Rockefeller’s Laboratory of DNA Replication. “However, it’s a recurring theme in science that nature does not always turn out to work the way you thought it did.”

Previously (left), the replisome’s two polymerases (green) were assumed to be below the helicase (tan), the enzyme that splits the DNA strands. The new images reveal one polymerase is located at the front of the helicase, causing one strand to loop backward as it is copied (right). [Brookhaven National Laboratory]

The researcher’s findings focused on the replisome found in eukaryotic organisms, a category that includes a broad swath of living things, including humans and other multicellular organisms. Over the past several decades, there has been an array of data describing the individual components comprising the complex nature of replisome. Yet, until now no pictures existed to show just how everything fit together.

“This work is a continuation of our long-standing research using electron microscopy to understand the mechanism of DNA replication, an essential function for every living cell,” explained co-senior author Huilin Li, Ph.D., biologist with joint appointments at Brookhaven Lab and Stony Brook University. “These new images show the fully assembled and fully activated ‘helicase’ protein complex—which encircles and separates the two strands of the DNA double helix as it passes through a central pore in the structure—and how the helicase coordinates with the two ‘polymerase’ enzymes that duplicate each strand to copy the genome.”

The image and implications from this study were described in a paper entitled “The architecture of a eukaryotic replisome,” published recently through Nature Structural & Molecular Biology.

Traditional models of DNA replication show the helicase enzyme moving along the DNA, separating the two strands of the double helix, with two polymerases located at the back where the DNA strand is split. In this configuration, the polymerases would add nucleotides to the side-by-side split ends as they move out of the helicase to form two new complete double helix DNA strands. However, the images that the researchers collected of intact replisomes revealed that only one of the polymerases is located at the back of the helicase. The other is on the front side of the helicase, where the helicase first encounters the double-stranded helix. This means that while one of the two split DNA strands is acted on by the polymerase at the back end, the other has to thread itself back through or around the helicase to reach the front-side polymerase before having its new complementary strand assembled.

“DNA replication is one of the most fundamental processes of life, so it is every biochemist’s dream to see what a replisome looks like,” stated lead author Jingchuan Sun, EM biologist in Dr. Li’s laboratory. “Our lab has expertise and a decade of experience using electron microscopy to study DNA replication, which has prepared us well to tackle the highly mobile therefore very challenging replisome structure. Working together with the O’Donnell lab, which has done beautiful, functional studies on the yeast replisome, our two groups brought perfectly complementary expertise to this project.”

The positioning of one polymerase at the front of the helicase suggests that it may have an unforeseen function—the possibilities of which the collaborative group of scientists is continuing to study. Whatever the function the offset polymerase ends up having, Drs. Li and O’Donnell hope that it will not only provide them better insight into the replication machinery but that they may uncover useful information that can be exploited for disease intervention.

“Clearly, further studies will be required to understand the functional implications of the unexpected replisome architecture reported here,” the scientists concluded.




Fifth Histone Found to Recruit Proteins for DNA Repair

Scientists at the University of Copenhagen say they have located a previously unknown function for histones, which allows for an improved understanding of how cells protect and repair DNA damages. This new discovery may be of great importance to the treatment of diseases caused by cellular changes such as cancer and immune deficiency syndrome.

The study (“Histone H1 couples initiation and amplification of ubiquitin signaling after DNA damage”) is published in Nature.

“I believe that there’s a lot of work ahead. It’s like opening a door onto a previously undiscovered territory filled with lots of exciting knowledge. The histones are incredibly important to many of the cells’ processes as well as their overall wellbeing,” said Niels Mailand, Ph.D., from the Novo Nordisk Foundation Center for Protein Research at the Faculty of Health and Medical Science.

Histones enable the tight packaging of DNA strands within cells. The strands are two meters in length and the cells usually about 100,000 times smaller. Generally speaking, there are five types of histones. Four of them are core histones and they are placed like beads on the DNA strands, which are curled up like a ball of wool within the cells. The role of the histones is already well described in research, and in addition to enabling the packaging of the DNA strands they also play a central part in practically every process related to the DNA-code, including repairing possibly damaged DNA.

The four core histones have tails and, among other things, they signal damage to the DNA and thus attract the proteins that help repair the damage. Between the histone “yarn balls” we find the fifth histone, Histone H1, but up until now its function has not been thoroughly examined.

Using a mass spectrometer, Dr. Mailand and his team have discovered that, surprisingly, the H1 histone also helps summon repair proteins.

“In international research, the primary focus has been on the core histones and their functionality, whereas little attention has been paid to the H1 histone, simply because we weren’t aware that it too influenced the repair process. Having discovered this function in the H1 constitutes an important piece of the puzzle of how cells protect their DNA, and it opens a door onto hitherto unknown and highly interesting territory,” noted Dr. Mailand.

He expects the discovery to lead to increased research into Histone H1 worldwide, which will lead to increased knowledge of cells’ abilities to repair possible damage to their DNA and thus increase our knowledge of the basis for diseases caused by cellular changes. It will also generate more knowledge about the treatment of these diseases.

“By mapping the function of the H1 histone, we will also learn more about the repair of DNA damages on a molecular level. In order to provide the most efficient treatment, we need to know how the cells prevent and repair these damages,” point out Dr. Mailand.


Cover All the Bases for Oligonucleotide Analysis

Stephen Luke

Synthetic oligonucleotides have emerged as promising therapeutic agents for the treatment of a variety of diseases, including viral infections and cancer. Researchers are looking at several classes of nucleic acids, such as antisense oligonucleotides, small interfering RNAs (siRNAs), and aptamers, for therapeutic applications.

However, various impurities – product-related, in the starting materials, and arising from incomplete capping of coupling reactions – must be identified and removed and postsynthesis processing must be monitored. Thus, a key challenge in the development and manufacture of oligonucleotide therapeutics is to establish analytical methods that are capable of separating and identifying impurities.

Exploring Better Options for Oligonucleotide LC Separations



Table 1. Options for oligonucleotide LC separations

Ion-pair, reversed-phase separation of the trityl-on oligos and is relatively simple to perform. This method separates the full-length target oligo, which still has the dMT group attached, from the deprotected failure sequences. The analytical information obtained is limited, so this is generally considered a purification method.

An alternate method, ion-exchange separations of the trityl-off, deprotected oligos uses the negative charge on the backbone of the oligo to facilitate the separation. Resolution is good for the shorter oligos but decreases with increasing chain length. Aqueous eluents are used but oligos are highly charged, and high concentrations of salt are needed to achieve elution from the column, making the technique unsuitable for use with LC/MS.

Finally, ion-pair, reversed-phase separation of the trityl-off, deprotected oligos makes use of organic solvents and mobile phase additives such as TEAA (triethylammonium acetate) or TEA-HFIP (triethylamine and hexafluoroisopropanol) to ion-pair with the negatively charged phosphodiester backbone of the oligonucleotide. High-performance columns deliver excellent resolution. What’s more, methods with volatile mobile phase constituents such as TEA-HFIP are suitable for use with LC/MS, providing useful information to help characterize oligonucleotide structures and sequences.

In Table 1 we summarize some of the options for oligonucleotide analysis by liquid chromatography.

Designed for ion-pair, reversed-phase separation of the trityl-off, deprotected oligos using either TEAA or TEA-HFIP mobile phases –Agilent AdvanceBio Oligonucleotide columns meet these challenges.



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What is the Future for Genomics in Clinical Medicine?

What is the Future for Genomics in Clinical Medicine?

Author and Curator: Larry H Bernstein, MD, FCAP



This is the last in a series of articles looking at the past and future of the genome revolution.  It is a revolution indeed that has had a beginning with the first phase discovery leading to the Watson-Crick model, the second phase leading to the completion of the Human Genome Project, a third phase in elaboration of ENCODE.  But we are entering a fourth phase, not so designated, except that it leads to designing a path to the patient clinical experience.
What is most remarkable on this journey, which has little to show in treatment results at this time, is that the boundary between metabolism and genomics is breaking down.  The reality is that we are a magnificent “magical” experience in evolutionary time, functioning in a bioenvironment, put rogether like a truly complex machine, and with interacting parts.  What are those parts – organelles, a genetic message that may be constrained and it may be modified based on chemical structure, feedback, crosstalk, and signaling pathways.  This brings in diet as a source of essential nutrients, exercise as a method for delay of structural loss (not in excess), stress oxidation, repair mechanisms, and an entirely unexpected impact of this knowledge on pharmacotherapy.  I illustrate this with some very new observations.

Gutenberg Redone

The first is a recent talk on how genomic medicine has constructed a novel version of the “printing press”, that led us out of the dark ages.


In our series The Creative Destruction of Medicine, I’m trying to get into critical aspects of how we can Schumpeter or reboot the future of healthcare by leveraging the big innovations that are occurring in the digital world, including digital medicine.

We have this big thing about evidence-based medicine and, of course, the sanctimonious randomized, placebo-controlled clinical trial. Well, that’s great if one can do that, but often we’re talking about needing thousands, if not tens of thousands, of patients for these types of clinical trials. And things are changing so fast with respect to medicine and, for example, genomically guided interventions that it’s going to become increasingly difficult to justify these very large clinical trials.

For example, there was a drug trial for melanoma and the mutation of BRAF, which is the gene that is found in about 60% of people with malignant melanoma. When that trial was done, there was a placebo control, and there was a big ethical charge asking whether it is justifiable to have a body count. This was a matched drug for the biology underpinning metastatic melanoma, which is essentially a fatal condition within 1 year, and researchers were giving some individuals a placebo.

The next observation is a progression of what he have already learned. The genome has a role is cellular regulation that we could not have dreamed of 25 years ago, or less. The role is far more than just the translation of a message from DNA to RNA to construction of proteins, lipoproteins, cellular and organelle structures, and more than a regulation of glycosidic and glycolytic pathways, and under the influence of endocrine and apocrine interactions. Despite what we have learned, the strength of inter-molecular interactions, strong and weak chemical bonds, essential for 3-D folding, we know little about the importance of trace metals that have key roles in catalysis and because of their orbital structures, are essential for organic-inorganic interplay. This will not be coming soon because we know almost nothing about the intracellular, interstitial, and intrvesicular distributions and how they affect the metabolic – truly metabolic events.

I shall however, use some new information that gives real cause for joy.

Reprogramming Alters Cells’ Fate

Kathy Liszewski
Gordon Conference  Report: June 21, 2012;32(11)
New and emerging strategies were showcased at Gordon Conference’s recent “Reprogramming Cell Fate” meeting. For example, cutting-edge studies described how only a handful of key transcription factors were needed to entirely reprogram cells.
M. Azim Surani, Ph.D., Marshall-Walton professor at the Gurdon Institute, University of Cambridge, U.K., is examining cellular reprogramming in a mouse model. Epiblast stem cells are derived from the early-stage embryonic stage after implantation of blastocysts, about six days into development, and retain the potential to undergo reversion to embryonic stem cells (ESCs) or to PGCs.”  They report two critical steps both of which are needed for exploring epigenetic reprogramming.  “Although there are two X chromosomes in females, the inactivation of one is necessary for cell differentiation. Only after epigenetic reprogramming of the X chromosome can pluripotency be acquired. Pluripotent stem cells can generate any fetal or adult cell type but are not capable of developing into a complete organism.”
The second read-out is the activation of Oct4, a key transcription factor involved in ESC development. The expression of Oct4 in epiSCs requires its proximal enhancer.  Dr. Surani said that their cell-based system demonstrates how a systematic analysis can be performed to analyze how other key genes contribute to the many-faceted events involved in reprogramming the germline.
Reprogramming Expressway
A number of other recent studies have shown the importance of Oct4 for self-renewal of undifferentiated ESCs. It is sufficient to induce pluripotency in neural tissues and somatic cells, among others. The expression of Oct4 must be tightly regulated to control cellular differentiation. But, Oct4 is much more than a simple regulator of pluripotency, according to Hans R. Schöler, Ph.D., professor in the department of cell and developmental biology at the Max Planck Institute for Molecular Biomedicine.
Oct4 has a critical role in committing pluripotent cells into the somatic cellular pathway. When embryonic stem cells overexpress Oct4, they undergo rapid differentiation and then lose their ability for pluripotency. Other studies have shown that Oct4 expression in somatic cells reprograms them for transformation into a particular germ cell layer and also gives rise to induced pluripotent stem cells (iPSCs) under specific culture conditions.
Oct4 is the gatekeeper into and out of the reprogramming expressway. By modifying experimental conditions, Oct4 plus additional factors can induce formation of iPSCs, epiblast stem cells, neural cells, or cardiac cells. Dr. Schöler suggests that Oct4 a potentially key factor not only for inducing iPSCs but also for transdifferention.  “Therapeutic applications might eventually focus less on pluripotency and more on multipotency, especially if one can dedifferentiate cells within the same lineage. Although fibroblasts are from a different germ layer, we recently showed that adding a cocktail of transcription factors induces mouse fibroblasts to directly acquire a neural stem cell identity.
Stem cell diagram illustrates a human fetus st...

Stem cell diagram illustrates a human fetus stem cell and possible uses on the circulatory, nervous, and immune systems. (Photo credit: Wikipedia)

English: Embryonic Stem Cells. (A) shows hESCs...

English: Embryonic Stem Cells. (A) shows hESCs. (B) shows neurons derived from hESCs. (Photo credit: Wikipedia)

Transforming growth factor beta (TGF-β) is a s...

Transforming growth factor beta (TGF-β) is a secreted protein that controls proliferation, cellular differentiation, and other functions in most cells. (Photo credit: Wikipedia)

Pioneer Transcription Factors

Pioneer transcription factors take the lead in facilitating cellular reprogramming and responses to environmental cues. Multicellular organisms consist of functionally distinct cellular types produced by differential activation of gene expression. They seek out and bind specific regulatory sequences in DNA. Even though DNA is coated with and condensed into a thick fiber of chromatin. The pioneer factor, discovered by Prof. KS Zaret at UPenn SOM in 1996, he says, endows the competence for gene activity, being among the first transcription factors to engage and pry open the target sites in chromatin.
FoxA factors, expressed in the foregut endoderm of the mouse,are necessary for induction of the liver program. They found that nearly one-third of the DNA sites bound by FoxA in the adult liver occur near silent genes

A Nontranscriptional Role for HIF-1α as a Direct Inhibitor of DNA Replication

ME Hubbi, K Shitiz, DM Gilkes, S Rey,….GL Semenza. Johns Hopkins University SOM
Sci. Signal 2013; 6(262) 10pgs. [DOI: 10.1126/scisignal.2003417] Nontranscriptional Role for HIF-1α as a Direct Inhibitor of DNA Replication/

Many of the cellular responses to reduced O2 availability are mediated through the transcriptional activity of hypoxia-inducible factor 1 (HIF-1). We report a role for the isolated HIF-1α subunit as an inhibitor of DNA replication, and this role was independent of HIF-1β and transcriptional regulation. In response to hypoxia, HIF-1α bound to Cdc6, a protein that is essential for loading of the mini-chromosome maintenance (MCM) complex (which has DNA helicase activity) onto DNA, and promoted the interaction between Cdc6 and the MCM complex. The binding of HIF-1α to the complex decreased phosphorylation and activation of the MCM complex by the kinase Cdc7. As a result, HIF-1α inhibited firing of replication origins, decreased DNA replication, and induced cell cycle arrest in various cell types. To whom correspondence should be addressed. E-mail:
Citation: M. E. Hubbi, Kshitiz, D. M. Gilkes, S. Rey, C. C. Wong, W. Luo, D.-H. Kim, C. V. Dang, A. Levchenko, G. L. Semenza, A Nontranscriptional Role for HIF-1α as a Direct Inhibitor of DNA Replication. Sci. Signal. 6, ra10 (2013).

Identification of a Candidate Therapeutic Autophagy-inducing Peptide

Nature 2013;494(7436).

Beth Levine and colleagues have constructed a cell-permeable peptide derived from part of an autophagy protein called beclin 1. This peptide is a potent inducer of autophagy in mammalian cells and in vivo in mice and was effective in the clearance of several viruses including chikungunya virus, West Nile virus and HIV-1.

Could this small autophagy-inducing peptide may be effective in the prevention and treatment of human diseases?

PR-Set7 Is a Nucleosome-Specific Methyltransferase that Modifies Lysine 20 of

Histone H4 and Is Associated with Silent Chromatin

K Nishioka, JC Rice, K Sarma, H Erdjument-Bromage, …, D Reinberg.   Molecular Cell, Vol. 9, 1201–1213, June, 2002, Copyright 2002 by Cell Press 

We have purified a human histone H4 lysine 20methyl-transferase and cloned the encoding gene, PR/SET07. A mutation in Drosophila pr-set7 is lethal: second in-star larval death coincides with the loss of H4 lysine 20 methylation, indicating a fundamental role for PR-Set7 in development. Transcriptionally competent regions lack H4 lysine 20 methylation, but the modification coincided with condensed chromosomal regions polytene chromosomes, including chromocenter euchromatic arms. The Drosophila male X chromosome, which is hyperacetylated at H4 lysine 16, has significantly decreased levels of lysine 20 methylation compared to that of females. In vitro, methylation of lysine 20 and acetylation of lysine 16 on the H4 tail are competitive. Taken together, these results support the hypothesis that methylation of H4 lysine 20 maintains silent chromatin, in part, by precluding neighboring acetylation on the H4 tail.

Next-Generation Sequencing vs. Microarrays

Shawn C. Baker, Ph.D., CSO of BlueSEQ
GEN Feb 2013
With recent advancements and a radical decline in sequencing costs, the popularity of next generation sequencing (NGS) has skyrocketed. As costs become less prohibitive and methods become simpler and more widespread, researchers are choosing NGS over microarrays for more of their genomic applications. The immense number of journal articles citing NGS technologies it looks like NGS is no longer just for the early adopters. Once thought of as cost prohibitive and technically out of reach, NGS has become a mainstream option for many laboratories, allowing researchers to generate more complete and scientifically accurate data than previously possible with microarrays.

Gene Expression

Researchers have been eager to use NGS for gene expression experiments for a detailed look at the transcriptome. Arrays suffer from fundamental ‘design bias’ —they only return results from those regions for which probes have been designed. The various RNA-Seq methods cover all aspects of the transcriptome without any a priori knowledge of it, allowing for the analysis of such things as novel transcripts, splice junctions and noncoding RNAs. Despite NGS advancements, expression arrays are still cheaper and easier when processing large numbers of samples (e.g., hundreds to thousands).
While NGS unquestionably provides a more complete picture of the methylome, whole genome methods are still quite expensive. To reduce costs and increase throughput, some researchers are using targeted methods, which only look at a portion of the methylome. Because details of exactly how methylation impacts the genome and transcriptome are still being investigated, many researchers find a combination of NGS for discovery and microarrays for rapid profiling.


They are interested in ease of use, consistent results, and regulatory approval, which microarrays offer. With NGS, there’s always the possibility of revealing something new and unexpected. Clinicians aren’t prepared for the extra information NGS offers. But the power and potential cost savings of NGS-based diagnostics is alluring, leading to their cautious adoption for certain tests such as non-invasive prenatal testing.
Perhaps the application that has made the least progress in transitioning to NGS is cytogenetics. Researchers and clinicians, who are used to using older technologies such as karyotyping, are just now starting to embrace microarrays. NGS has the potential to offer even higher resolution and a more comprehensive view of the genome, but it currently comes at a substantially higher price due to the greater sequencing depth. While dropping prices and maturing technology are causing NGS to make headway in becoming the technology of choice for a wide range of applications, the transition away from microarrays is a long and varied one. Different applications have different requirements, so researchers need to carefully weigh their options when making the choice to switch to a new technology or platform. Regardless of which technology they choose, genomic researchers have never had more options.

Sequencing Hones In on Targets

Greg Crowther, Ph.D.

GEN Feb 2013

Cliff Han, PhD, team leader at the Joint Genome Institute in the Los Alamo National Lab, was one of a number of scientists who made presentations regarding target enrichment at the “Sequencing, Finishing, and Analysis in the Future” (SFAF) conference in Santa Fe, which was co-sponsored by the Los Alamos National Laboratory and DOE Joint Genome Institute. One of the main challenges is that of target enrichment: the selective sequencing of genomic or transcriptomic regions. The polymerase chain reaction (PCR) can be considered the original target-enrichment technique and continues to be useful in contexts such as genome finishing. “One target set is the unique gaps—the gaps in the unique sequence regions. Another is to enrich the repetitive sequences…ribosomal RNA regions, which together are about 5 kb or 6 kb.” The unique-sequence gaps targeted for PCR with 40-nucleotide primers complementary to sequences adjacent to the gaps, did not yield the several-hundred-fold enrichment expected based on previously published work. “We got a maximum of 70-fold enrichment and generally in the dozens of fold of enrichment,” noted Dr. Han.

“We enrich the genome, put the enriched fragments onto the Pacific Biosciences sequencer, and sequence the repeats,” continued Dr. Han. “In many parts of the sequence there will be a unique sequence anchored at one or both ends of it, and that will help us to link these scaffolds together.” This work, while promising, will remain unpublished for now, as the Joint Genome Institute has shifted its resources to other projects.
At the SFAF conference Dr. Jones focused on going beyond basic target enrichment and described new tools for more efficient NGS research. “Hybridization methods are flexible and have multiple stop-start sites, and you can capture very large sizes, but they require library prep,” said Jennifer Carter Jones, Ph.D., a genomics field applications scientist at Agilent. “With PCR-based methods, you have to design PCR primers and you’re doing multiplexed PCR, so it’s limited in the size that you can target. But the workflow is quick because there’s no library preparation; you’re just doing PCR.” She discussed Agilent’s recently acquired HaloPlex technology, a hybrid system that includes both a hybridization step and a PCR step. Because no library preparation is required, sequencing results can be obtained in about six hours, making it suitable for clinical uses. However, the hybridization step allows capture of targets of up to 5 megabases—longer than purely PCR-based methods can deliver. The Agilent talk also provided details on the applications of SureSelect, the company’s hybridization technology, to Methyl-Seq and RNA-Seq research. With this technology, 120-mer baits hybridize to targets, then are pulled down with streptavidin-coated magnetic beads.
These are selections from the SFAF conference, which is expected to be a boost to work on the microbiome, and lead to infectious disease therapeutic approaches.


We have finished a breathtaking ride through the genomic universe in several sessions.  This has been a thorough review of genomic structure and function in cellular regulation.  The items that have been discussed and can be studied in detail include:

  1.  the classical model of the DNA structure
  2. the role of ubiquitinylation in managing cellular function and in autophagy, mitophagy, macrophagy, and protein degradation
  3. the nature of the tight folding of the chromatin in the nucleus
  4. intramolecular bonds and short distance hydrophobic and hydrophilic interactions
  5. trace metals in molecular structure
  6. nuclear to membrane interactions
  7. the importance of the Human Genome Project followed by Encode
  8. the Fractal nature of chromosome structure
  9. the oligomeric formation of short sequences and single nucletide polymorphisms (SNPs)and the potential to identify drug targets
  10. Enzymatic components of gene regulation (ligase, kinases, phosphatases)
  11. Methods of computational analysis in genomics
  12. Methods of sequencing that have become more accurate and are dropping in cost
  13. Chromatin remodeling
  14. Triplex and quadruplex models not possible to construct at the time of Watson-Crick
  15. sequencing errors
  16. propagation of errors
  17. oxidative stress and its expected and unintended effects
  18. origins of cardiovascular disease
  19. starvation and effect on protein loss
  20. ribosomal damage and repair
  21. mitochondrial damage and repair
  22. miscoding and mutational changes
  23. personalized medicine
  24. Genomics to the clinics
  25. Pharmacotherapy horizons
  26. driver mutations
  27. induced pluripotential embryonic stem cell (iPSCs)
  28. The association of key targets with disease
  29. The real possibility of moving genomic information to the bedside
  30. Requirements for the next generation of electronic health record to enable item 29

Other Related articles on this Open Access Online Scientific Journal, include the following:   SSaha RSaxena   ASarkar and RSaxena    LHB  SJWilliams ALev-Ari  SJWilliams  TBarliya

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From Molecular Biology to Translational Medicine: How Far Have We Come, and Where Does It Lead Us?

The Initiation and Growth of Molecular Biology and Genomics, Part I

Curator: Larry H Bernstein, MD, FCAP

Introduction and purpose

This material will cover the initiation phase of molecular biology, Part I; to be followed by the Human Genome Project, Part II; and concludes with Ubiquitin, it’s Role in Signaling and Regulatory Control, Part III.
This article is first a continuation of a previous discussion on the role of genomics in discovery of therapeutic targets titled Directions for genomics in personalized medicine

The previous article focused on key drivers of cellular proliferation, stepwise mutational changes coinciding with cancer progression, and potential therapeutic targets for reversal of the process. It also covers the race to delineation of the Human Genome, discovery methods and fundamental genomic patterns that are ancient in both animal and plant speciation.

This article reviews the web-like connections between early and later discoveries, as significant finding has led to novel hypotheses and many more findings over the last 75 years. This largely post WWII revolution has driven our understanding of biological and medical processes at an exponential pace owing to successive discoveries of chemical structure, the basic building blocks of DNA and proteins, of nucleotide and protein-protein interactions, protein folding, allostericity, genomic structure, DNA replication, nuclear polyribosome interaction, and metabolic control. In addition, the emergence of methods for copying, removal and insertion, and improvements in structural analysis as well as developments in applied mathematics have transformed the research framework.

In the Beginning

During the Second World War we had the discoveries of physics and the emergence out of the Manhattan Project of radioactive nuclear probes from E.O. Lawrence University of California Berkeley Laboratory. The use of radioactive isotopes led to the development of biochemistry and isolation of nucleotides, nucleosides, enzymes, and filling in of details of pathways for photosynthesis, for biosynthesis, and for catabolism.
Perhaps a good start of the journey is a student of Neils Bohr named Max Delbruck (September 4, 1906 – March 9, 1981), who won the Nobel prize for discovering that bacteria become resistant to viruses (phages) as a result of genetic mutations, founded a new discipline called Molecular Biology, lifting the experimental work in Physiology to a systematic experimentation in biology with the rigor of Physics using radiation and virus probes on selected cells. In 1937 he turned to research on the genetics of Drosophila melanogaster at Caltech, and two years later he coauthored a paper, “The growth of bacteriophage”, reporting that the viruses replicate in one step, not exponentially. In 1942, he and Salvador Luria of Indiana University demonstrated that bacterial resistance to virus infection is mediated by random mutation. This research, known as the Luria-Delbrück experiment, notably applied mathematics to make quantitative predictions, and earned them the 1969 Nobel Prize in Physiology or Medicine, shared with Alfred Hershey. His inferences on genes’ susceptibility to mutation was relied on by physicist Erwin Schrödinger in his 1944 book, What Is Life?, which conjectured genes were an “aperiodic crystal” storing code-script and influenced Francis Crick and James D. Watson in their 1953 identification of cellular DNA’s molecular structure as a double helix.

Watson-Crick Double Helix Model

A new understanding of heredity and hereditary disease was possible once it was determined that DNA consists of two chains twisted around each other, or double helixes, of alternating phosphate and sugar groups, and that the two chains are held together by hydrogen bonds between pairs of organic bases—adenine (A) with thymine (T), and guanine (G) with cytosine (C). Modern biotechnology also has its basis in the structural knowledge of DNA—in this case the scientist’s ability to modify the DNA of host cells that will then produce a desired product, for example, insulin.
The background for the work of the four scientists was formed by several scientific breakthroughs:

  1. the progress made by X-ray crystallographers in studying organic macromolecules;
  2. the growing evidence supplied by geneticists that it was DNA, not protein, in chromosomes that was responsible for heredity;
  3. Erwin Chargaff’s experimental finding that there are equal numbers of A and T bases and of G and C bases in DNA;
  4. and Linus Pauling’s discovery that the molecules of some proteins have helical shapes.

In 1962 James Watson (b. 1928), Francis Crick (1916–2004), and Maurice Wilkins (1916–2004) jointly received the Nobel Prize in physiology or medicine for their 1953 determination of the structure of deoxyribonucleic acid (DNA), performed with a knowledge of Chargaff’s ratios of the bases in DNA and having  access to the X-ray crystallography of Maurice Wilkins and Rosalind Franklin at King’s College London. Because the Nobel Prize can be awarded only to the living, Wilkins’s colleague Rosalind Franklin (1920–1958), who died of cancer at the age of 37, could not be honored.
Of the four DNA researchers, only Rosalind Franklin had any degrees in chemistry. Franklin completed her degree in 1941 in the middle of World War II and undertook graduate work at Cambridge with Ronald Norrish, a future Nobel Prize winner. She returning to Cambridge after a year of war service, presented her work and received the PhD in physical chemistry. Franklin then learned the  X-ray crystallography in Paris and rapidly became a respected authority in this field. Returning to returned to England to King’s College London in 1951, her charge was to upgrade the X-ray crystallographic laboratory there for work with DNA.

bt2304  Rosalind Franklin, crystallographer

Cold Spring Harbor Laboratory

I digress to the beginnings of the Cold Spring Harbor Laboratory. A significant part of the Laboratory’s life revolved around education with its three-week-long Phage Course, taught first in 1945 by Max Delbruck, the German-born, theoretical-physicist-turned-biologist. James D Watson first came to Cold Spring Harbor Laboratory with his thesis advisor, Salvador Luria, in the summer of 1948. Over its more than 25-year history, the Phage Course was the training ground for many notable scientists. The Laboratory’s annual scientific Symposium, has provided a unique highly interactive education about the exciting field of “molecular” biology. The 1953 symposium featured Watson coming from England to give the first public presentation of the DNA double helix. When he became the Laboratory’s director in 1968 he was determined to make the Laboratory an important center for advancing molecular biology, and he focused his energy on bringing large donations to the enterprise CSHNL. It became a magnate for future discovery at which James D. Watson became the  Director in 1968, and later the Chancellor. This contribution has as great an importance as his Nobel Prize discovery.

Biochemistry and Molecular Probes comes into View

Moreover, at the same time, the experience of Nathan Kaplan and Martin Kamen at Berkeley working with radioactive probes was the beginning of an establishment of Lawrence-Livermore Laboratories role in metabolic studies, as reported in the previous paper. A collaboration between Sid Collowick, NO Kaplan and Elizabeth Neufeld at the McCollum Pratt Institute led to the transferase reaction between the two main pyridine nucleotides.  Neufeld received a PhD a few years later from the University of California, Berkeley, under William Zev Hassid for research on nucleotides and complex carbohydrates, and did postdoctoral studies on non-protein sulfhydryl compounds in mitosis. Her later work at the NIAMDG on mucopolysaccharidoses. The Lysosomal Storage Diseases opened a new chapter on human genetic diseases when she found that the defects in Hurler and Hunter syndromes were due to decreased degradation of the mucopolysaccharides. When an assay became available for α-L-iduronidase in 1972, Neufeld was able to show that the corrective factor for Hurler syndrome that accelerates degradation of stored sulfated mucopolysaccharides was α-L-iduronidase.


The Hurler Corrective Factor. Purification and Some Properties (Barton, R. W., and Neufeld, E. F. (1971) J. Biol. Chem. 246, 7773–7779)
The Sanfilippo A Corrective Factor. Purification and Mode of Action (Kresse, H., and Neufeld, E. F. (1972) J. Biol. Chem. 247, 2164–2170)

I mention this for two reasons:
[1] We see a huge impetus for nucleic acids and nucleotides research growing in the 1950’s with a post WWII emergence of work on biological structure.
[2] At the same time, the importance of enzymes in cellular metabolic processes runs parallel to that of the genetic code.

In 1959 Arthur Kornberg was a recipient of the Nobel prize for Physiology or Medicine based on his discovery of “the mechanisms in the biological synthesis of deoxyribonucleic acid” (DNA polymerase) together with Dr. Severo Ochoa of New York University. In the next 20 years Stanford University Department of Biochemistry became a top rated graduate program in biochemistry. Today, the Pfeffer Lab is distinguished for research into how human cells put receptors in the right place through Rab GTPases that regulate all aspects of receptor trafficking. Steve Elledge (1984-1989) at Harvard University is one of  its graduates from the 1980s.

Transcription –RNA and the ribosome

In 2006, Roger Kornberg was awarded the Nobel Prize in Chemistry for identifying the role of RNA polymerase II and other proteins in transcribing DNA. He says that the process is something akin to a machine. “It has moving parts which function in synchrony, in appropriate sequence and in synchrony with one another”. The Kornbergs were the tenth family with closely-related Nobel laureates.  The 2009 Nobel Prize in Chemistry was awarded to Venki Ramakrishnan, Tom Steitz, and Ada Yonath for crystallographic studies of the ribosome. The atomic resolution structures of the ribosomal subunits provide an extraordinary context for understanding one of the most fundamental aspects of cellular function: protein synthesis. Research on protein synthesis began with studies of microsomes, and three papers were published on the atomic resolution structures of the 50S and 30S the atomic resolution of structures of ribosomal subnits in 2000. Perhaps the most remarkable and inexplicable feature of ribosome structure is that two-thirds of the mass is composed of large RNA molecules, the 5S, 16S, and 23S ribosomal RNAs, and the remaining third is distributed among ~50 relatively small and innocuous proteins. The first step on the road to solving the ribosome structure was determining the primary structure of the 16S and 23S RNAs in Harry Noller’s laboratory. The sequences were rapidly followed by secondary structure models for the folding of the two ribosomal RNAs, in collaboration with Carl Woese, bringing the ribosome structure into two dimensions. The RNA secondary structures are characterized by an elaborate series of helices and loops of unknown structure, but other than the insights offered by the structure of transfer RNA (tRNA), there was no way to think about folding these structures into three dimensions. The first three-dimensional images of the ribosome emerged from Jim Lake’s reconstructions from electron microscopy (EM) (Lake, 1976).

Ada Yonath reported the first crystals of the 50S ribosomal subunit in 1980, a crucial step that would require almost 20 years to bring to fruition (Yonath et al., 1980). Yonath’s group introduced the innovative use of ribosomes from extremophilic organisms. Peter Moore and Don Engelman applied neutron scattering techniques to determine the relative positions of ribosomal proteins in the 30S ribosomal subunit at the same time. Elegant chemical footprinting studies from the Noller laboratory provided a basis for intertwining the RNA among the ribosomal proteins, but there was still insufficient information to produce a high resolution structure, but Venki Ramakrishnan, in Peter Moore’s laboratory did it with deuterated ribosome reconstitutions. Then the Yale group was ramping up its work on the H. marismortui crystals of the 50S subunit. Peter Moore had recruited long-time colleague Tom Steitz to work on this problem and Steitz was about to complete the final event in the pentathlon of Crick’s dogma, having solved critical structures of DNA polymerases, the glutaminyl tRNA-tRNA synthetase complex, HIV reverse transcriptase, and T7 RNA polymerase. In 1999 Steitz, Ramakrishnan, and Yonath all presented electron density maps of subunits at approximately 5 Å resolution, and the Noller group presented 10 Å electron density maps of the Thermus 70S ribosome. Peter Moore aptly paraphrased Churchill, telling attendees that this was not the end, but the end of the beginning. Almost every nucleotide in the RNA is involved in multiple stabilizing interactions that form the monolithic tertiary structure at the heart of the ribosome.
Williamson J. The ribosome at atomic resolution. Cell 2009; 139:1041-1043.

This opened the door to new therapies.  For example, in 2010 it was reported that Numerous human genes display dual coding within alternatively spliced regions, which give rise to distinct protein products that include segments translated in more than one reading frame. To resolve the ensuing protein structural puzzle, we identified human genes with alternative splice variants comprising a dual coding region at least 75 nucleotides in length and analyzed the structural status of the protein segments they encode. The inspection of their amino acid composition and predictions by the IUPred and PONDR® VSL2 algorithms suggest a high propensity for structural disorder in dual-coding regions.
Kovacs E, Tompa P, liliom K, and Kalmar L. Dual coding in alternative reading frames correlates with intrinsic protein disorder. PNAS 2010.

In 2012, it was shown that drug-bound ribosomes can synthesize a distinct subset of cellular polypeptides. The structure of a protein defines its ability to thread through the antibiotic-obstructed tunnel. Synthesis of certain polypeptides that initially bypass translational arrest can be stopped at later stages of elongation while translation of some proteins goes to completion. (Kannan K, Vasquez-Laslop N, and Mankin AS. Selective Protein Synthesis by Ribosomes with a Drug-Obstructed Exit Tunnel. Cell 2012; 151; 508-520.)

Mobility of genetic elements

Barbara McClintock received the Nobel Prize for Medicine for the discovery of the mobility of genetic elements, work that been done in that period. When transposons were demonstrated in bacteria, yeast and other organisms, Barbara rose to a stratospheric level in the general esteem of the scientific world, but she was uncomfortable about the honors. It was sufficient to have her work understood and acknowledged. Prof. Howard Green said of her, “There are scientists whose discoveries greatly transcend their personalities and their humanity. But those in the future who will know of Barbara only her discoveries will know only her shadow”.
“In Memoriam – Barbara McClintock”. 5 Feb 2013

She introduced her Nobel Lecture in 1983 with the following observation: “An experiment conducted in the mid-nineteen forties prepared me to expect unusual responses of a genome to challenges for which the genome is unprepared to meet in an orderly, programmed manner. In most known instances of this kind, the types of response were not predictable in advance of initial observations of them. It was necessary to subject the genome repeatedly to the same challenge in order to observe and appreciate the nature of the changes it induces…a highly programmed sequence of events within the cell that serves to cushion the effects of the shock. Some sensing mechanism must be present in these instances to alert the cell to imminent danger, and to set in motion the orderly sequence of events that will mitigate this danger”. She goes on to consider “early studies that revealed programmed responses to threats that are initiated within the genome itself, as well as others similarly initiated, that lead to new and irreversible genomic modifications. These latter responses, now known to occur in many organisms, are significant for appreciating how a genome may reorganize itself when faced with a difficulty for which it is unprepared”.

An experiment with Zea conducted in the summer of 1944 alerted her to the mobility of specific components of genomes involved the entrance of a newly ruptured end of a chromosome into a telophase nucleus. This experiment commenced with the growing of approximately 450 plants in the summer of 1944, each of which had started its development with a zygote that had received from each parent a chromosome with a newly ruptured end of one of its arms. The design of the experiment required that each plant be self-pollinated to isolate from the self-pollinated progeny new mutants that were expected to appear, and confine them to locations within the ruptured arm of a chromosome. Each mutant was expected to reveal the phenotype produced by a minute homozygous deficiency. Their modes of origin could be projected from the known behavior of broken ends of chromosomes in successive mitoses. Forty kernels from each self-pollinated ear were sown in a seedling bench in the greenhouse during the winter of 1944-45.

Some seedling mutants of the type expected overshadowed by segregants exhibiting bizarre phenotypes. These were variegated for type and degree of expression of a gene. Those variegated expressions given by genes associated with chlorophyll development were startingly conspicuous. Within any one progeny chlorophyll intensities, and their pattern of distribution in the seedling leaves, were alike. Between progenies, however, both the type and the pattern differed widely.

The effect of X-rays on chromosomes

Initial studies of broken ends of chromosomes began in the summer of 1931. By 1931, means of studying the beads on a string hypothesis was provided by newly developed methods of examining the ten chromosomes of the maize complement in microsporocytes in meiosis. The ten bivalent chromosomes are elongated in comparison to their metaphase lengths. Each chromosome

  • is identifiable by its relative length,
  • by the location of its centromere, which is readily observed at the pachytene stage, and
  • by the individuality of the chromomeres strung along the length of each chromosome.

At that time maize provided the best material for locating known genes along a chromosome arm, and also for precisely determining the break points in chromosomes that had undergone various types of rearrangement, such as translocations, inversions, etc.
The recessive phenotypes in the examined plants arose from loss of a segment of a chromosome that carried the wild-type allele, and X-rays were responsible for inducing these deficiencies. A conclusion of basic significance could be drawn from these observations:

  1. broken ends of chromosomes will fuse, 2-by-2, and
  2. any broken end with any other broken end.

This principle has been amply proved in a series of experiments conducted over the years. In all such instances the break must sever both strands of the DNA double helix. This is a “double-strand break” in modern terminology. That two such broken ends entering a telophase nucleus will find each other and fuse, regardless of the initial distance that separates them, soon became apparent.

During the summer of 1931 she had seen plants in the maize field that showed variegation patterns resembling the one described for Nicotiana.  Dr. McClintock was interested in selecting the variegated plants to determine the presence of a ring chromosome in each, and in the summer of 1932 with Dr. Stadler’s generous cooperation from Missouri, she had the opportunity to examine such plants. Each plant had a ring chromosome, but It was the behavior of this ring that proved to be significant. It revealed several basic phenomena. The following was noted:

In the majority of mitoses

  • replication of the ring chromosome produced two chromatids completely free from each other
  • could separate without difficulty in the following anaphase.
  • sister strand exchanges do occur between replicated or replicating chromatids
  • the frequency of such events increases with increase in the size of the ring.
  • these exchanges produce a double-size ring with two centromeres.
  • Mechanical rupture occurs in each of the two chromatid bridges formed at anaphase by passage of the two centromeres on the double-size ring to opposite poles of the mitotic spindle.
  • The location of a break can be at any one position along any one bridge.
  • The broken ends entering a telophase nucleus then fuse.
  • The size and content of each newly constructed ring depend on the position of the rupture that had occurred in each bridge.
  1. The conclusion was that cells sense the presence in their nuclei of ruptured ends of chromosomes
  2. then activate a mechanism that will bring together and then unite these ends
  3. this will occur regardless of the initial distance in a telophase nucleus that separated the ruptured ends.

The ability of a cell to

  • sense these broken ends,
  • to direct them toward each other, and
  • then to unite them so that the union of the two DNA strands is correctly oriented,
  • is a particularly revealing example of the sensitivity of cells to all that is going on within them.

Evidence from gave unequivocal support for the conclusion that broken ends will find each other and fuse. The challenge is met by a programmed response. This may be necessary, as

  1. both accidental breaks and
  2. programmed breaks may be frequent.
  3. If not repaired, such breaks could lead to genomic deficiencies having serious consequences.

A cell capable of repairing a ruptured end of a chromosome must sense the presence of this end in its nucleus. This sensing

  • activates a mechanism that is required for replacing the ruptured end with a functional telomere.
  • that such a mechanism must exist was revealed by a mutant that arose in the stocks.
  • this mutant would not allow the repair mechanism to operate in the cells of the plant.

Entrance of a newly ruptured end of a chromosome into the zygote is followed by the chromatid type of breakage-fusion-bridge cycle throughout mitoses in the developing plant.
This suggested that the repair mechanism in the maize strains is repressed in cells producing

  • the male and female gametophytes and
  • also in the endosperm,
  • but is activated in the embryo.

The extent of trauma perceived by cells

  • whose nuclei receive a single newly ruptured end of a chromosome that the cell cannot repair,
  • and the speed with which this trauma is registered, was not appreciated until the winter of 1944-45.

By 1947 it was learned that the bizarre variegated phenotypes that segregated in many of the self-pollinated progenies grown on the seedling bench in the fall and winter of 1944-45, were due to the action of transposable elements. It seemed clear that

  • these elements must have been present in the genome,
  • and in a silent state previous to an event that activated one or another of them.

She concluded that some traumatic event was responsible for these activations. The unique event in the history of these plants relates to their origin. Both parents of the plants grown in 1944 had contributed a chromosome with a newly ruptured end to the zygote that gave rise to each of these plants.
Detection of silent elements is now made possible with the aid of DNA cloning method. Silent AC (Activator) elements, as well as modified derivatives of them, have already been detected in several strains of maize. When other transposable elements are cloned it will be possible to compare their structural and numerical differences among various strains of maize. In any one strain of maize the number of silent but potentially transposable elements, as well as other repetitious DNAs, may be observed to change, and most probably in response to challenges not yet recognized.
Telomeres are especially adapted to replicate free ends of chromosomes. When no telomere is present, attempts to replicate this uncapped end may be responsible for the apparent “fusions” of the replicated chromatids at the position of the previous break as well as for perpetuating the chromatid type of breakage-fusion-bridge cycle in successive mitoses.
In conclusion, a genome may react to conditions for which it is unprepared, but to which it responds in a totally unexpected manner. Among these is

  • the extraordinary response of the maize genome to entrance of a single ruptured end of a chromosome into a telophase nucleus.
  • It was this event that was responsible for activations of potentially transposable elements that are carried in a silent state in the maize genome.
  • The mobility of these activated elements allows them to enter different gene loci and to take over control of action of the gene wherever one may enter.

Because the broken end of a chromosome entering a telophase nucleus can initiate activations of a number of different potentially transposable elements,

  • the modifications these elements induce in the genome may be explored readily.

In addition to

modifying gene action, these elements can

  • restructure the genome at various levels,
  • from small changes involving a few nucleotides,
  • to gross modifications involving large segments of chromosomes, such as
  1. duplications,
  2. deficiencies,
  3. inversions,
  4. and other reorganizations.

In the future attention undoubtedly will be centered on the genome, and with greater appreciation of its significance as a highly sensitive organ of the cell,

  • monitoring genomic activities and correcting common errors,
  • sensing the unusual and unexpected events,
  • and responding to them,
  • often by restructuring the genome.

We know about the elements available for such restructuring. We know nothing, however, about

  • how the cell senses danger and instigates responses to it that often are truly remarkable.


In 2009 the Nobel Prize in Physiology or Medicine was awarded to Elizabeth Blackburn, Carol Greider and Jack Szoztak for the discovery of Telomerase. This recognition came less than a decade after the completion of the Human Genome Project previously discussed. Prof. Blackburn acknowledges a strong influence coming from the work of Barbara McClintock. The discovery is tied to the pond organism Tetrahymena thermophila, and studies of yeast cells. Blackburn was drawn to science after reading the biography of Marie Curie by her daughter, Irina, as a child. She recalls that her Master’s mentor while studying the metabolism of glutamine in the rat liver, thought that every experiment should have the beauty and simplicity of a Mozart sonata. She did her PhD at the distinguished Laboratory for Molecular Biology at Cambridge, the epicenter of molecular biology sequencing the regions of bacteriophage phiX 174, a single stranded DNA bacteriophage. Using Fred Sanger’s methods to piece together RNA sequences she showed the first sequence of a 48 nucleotide fragment to her mathematical-gifted Cambridge cousin, who pointed out repeats of DNA sequence patterns! She worked on the sequencing of the DNA at the terminal regions of  the short “minichromosomes” of the ciliated protozoan Tetrahymena thermophile at Yale in 1975. She continued her research begun at Yale at UCSF funded by the NIH based on an intriguing audiogram showing telomeric DNA in Tetrahymena.
I describe the work as follows:

  • Prof. Blackburn incorporated 32P isotope labelled deoxynucleoside residues into the rDNA molecules for DNA repair enzymatic reactions and found that
  • the end regions were selectively labeled by combinations of 32P isotope radiolabled nucleoside triphosphate, and by mid-year she had an audiogram of the depurination products.
  • The audiogram showed sequences of 4 cytosine residues flanked by either an adenosine or a guanosine residue.
  • In 1976 she had deduced a sequence consisting of a tandem array of CCCAA repeats, and subsequently separated the products on a denaturing gel electrophoresis that appeared as tiger stripes extending up the gel.
  • The size of each band was 6 bases more than the band below it.

Telomere must have a telomerase!

The discovery of the telomerase enzyme activity was done by the Prize co-awardee, Carol Greider. They were trying to decipher the structure right at the termini of telomeres of both cliliated protozoans and yeast plasmids. The view that in mammalian telomeres there is a long protruding G-rich strand does not take into account the clear evidence for the short C strand repeat oligonucleotides that she discovered. This was found for both the Tetrahymena rDNA minichromosome molecules and linear plasmids purified from yeast.
In contrast to nucleosomal regions of chromosomes, special regions of DNA, for example

  • promoters that must bind transcription initiation factors that control transcription, have proteins other than the histones on them.
  • The telomeric repeat tract turned out to be such a non-nucleosomal region.

They  found that by clipping up chromatin using an enzyme that cuts the linker between neighboring nucleosomes,

  • it cut up the bulk of the DNA into nucleosome-sized pieces
  • but left the telomeric DNA tract as a single protected chunk.

The resulting complex of the telomeric DNA tract plus its bound cargo of protective proteins behaved very differently, from nucleosomal chromatin, and concluded that it had no histones or nucleosomes.

Any evidence for a protein on the bulk of the rDNA molecule ends, such as their behavior in gel electrophoresis and the appearance of the rDNA molecules under the electron microscope, was conspicuously lacking. This was reassuring that there was no covalently attached protein at the very ends of this minichoromosome. Despite considerable work, she was unable to determine what protein(s) would co-purify with the telomeric repeat tract DNA of Tetrahymena. It was yeast genetics and approaches done by others that turned out to provide the next great leaps forward in understanding telomeric proteins. Carol Greider, her colleague, noticed the need to scale up the telomerase activity preparations and they used a very large glass column for preparative gel filtration chromatography.

Jack W Szostak at the Howard Hughes Medical Institue at Harvard shared in the 2009 Nobel Prize. He became interested in molecular biology taking a course on the frontiers of Molecular Biology and reading about the experiments of Meselson-Stahl barely a decade earlier, and learned how the genetic code had been unraveled. The fact that one could deduce, from measurements of the radioactivity in fractions from a centrifuge tube, the molecular details of DNA replication, transcription and translation was astonishing. A highlight of his time at McGill was the open-book, open-discussion final exam in this class, in which the questions required the intense collaboration of groups of students.

At Cornell, Ithaca, he collaborated with  John Stiles and they came up with a specific idea to chemically synthesize a DNA oligonucleotide of sufficient length that it would hybridize to a single sequence within the yeast genome, and then to use it as an mRNA and gene specific probe. At the time, there was only one short segment of the yeast genome for which the DNA sequence was known,

  • the region coding for the N-terminus of the iso-1 cytochrome c protein,

intensively studied by Fred Sherman
The Sherman lab, in a tour de force of genetics and protein chemistry, had isolated

  • double-frameshift mutants in which the N-terminal region of the protein was translated from out-of-frame codons.
  • Protein sequencing of the wild type and frame-shifted mutants allowed them to deduce 44 nucleotides of DNA sequence.

If they could prepare a synthetic oligonucleotide that was complementary to the coding sequence, they could use it to detect the cytochrome-c mRNA and gene. At the time, essentially all experiments on mRNA were done on total cellular mRNA. Ray Wu was already well known for determining the sequence of the sticky ends of phage lambda, the first ever DNA to be sequenced, and his lab was deeply involved in the study of enzymes that could be used to manipulate and sequence DNA more effectively, but would not take on a project from another laboratory. So John went to nearby Rochester to do postdoctoral work with Sherman, and he was able to transfer to Ray Wu’s laboratory. In order to carry out his work, Ray Wu sent him to Saran Narang’s lab in Ottawa, and he received training there under Keichi Itakura, who synthesized the Insulin gene. A few months later, he received several milligrams of our long sought 15-mer. In collaboration with John Stiles and Fred Sherman, who sent us RNA and DNA samples from appropriate yeast strains, they were able to use the labeled 15-mer as a probe to detect the cyc1 mRNA, and later the gene itself. He notes that one of the delights of the world of science is that it is filled with people of good will who are more than happy to assist a student or colleague by teaching a technique or discussing a problem. He remained in Ray’s lab after completion of the PhD upon the arrival of Rodney Rothstein from Sherman’s lab in Rochester, who introduced him to yeast genetics, and he was prepared for the next decade of work on yeast.

  • first in recombination studies, and
  • later in telomere studies and other aspects of yeast biology.

His studies of recombination in yeast were enabled by the discovery, in Gerry Fink’s lab at Cornell, of a way to introduce foreign DNA into yeast. These pioneering studies of yeast transformation showed that circular plasmid DNA molecules could on occasion become integrated into yeast chromosomal DNA by homologous recombination.

  • His studies of unequal sister chromatid exchange in rDNA locus resulted in his first publication in the field of recombination.

The idea that you could increase transformation frequency by cutting the input DNA was pleasingly counterintuitive and led us to continue our exploration of this phenomenon. He gained an appointment to the Sidney-Farber Cancer Institute due to the interest of Prof. Ruth Sager, who gathered together a great group of young investigators. In work spearheaded by his first graduate student, Terry Orr-Weaver, on

  • double-strand breaks in DNA
  • and their repair by recombination (and continuing interaction with Rod Rothstein),
  • they were attracted to what kinds of reactions occur at the DNA ends.

It was at a Gordon Conference that he was excited hearing a talk by Elizabeth Blackburn on her work on telomeres in Tetrahymena.

  • This led to a collaboration testing the ability of Tetrahymena telomers to function in yeast.
  • He performed the experiments himself, and experienced the thrill of being the first to know that our wild idea had worked.
  • It was clear from that point on that a door had been opened and that they were going to be able to learn a lot about telomere function from studies in yeast.
  • Within a short time he was able to clone bona fide yeast telomeres, and (in a continuation of the collaboration with Liz Blackburn’s lab)
  • they obtained the critical sequence information that led (them) to propose the existence of the key enzyme, telomerase.

A fanciful depiction evoking both telomere dynamics and telomere researchers, done by the artist Julie Newdoll in 2008, elicits the idea of a telomere as an ancient Sumarian temple-like hive, tended by a swarm of ancient Sumarian Bee-goddesses against a background of clay tablets inscribed with DNA sequencing gel-like bands.
Dr. Blackburn recalls owing much to Barbara McClintock for her scientific findings, but also, Barbara McClintock also gave her advice in a conversation with her in 1977, during which

  • she had unexpected findings with the rDNA end sequences.
  • Dr. McClintock urged her to trust in intuition about the scientific research results.

This advice was surprising then because intuitive thinking was not something that she accepted to be a valid aspect of being a biology researcher.
MLA style: “Elizabeth H. Blackburn – Biographical”. 5 Feb 2013.


In this Part I of a series of 3, I have described the

  • emergence of Molecular Biology and
  • closely allied work on the mechanism of Cell Replication and
  • the dependence of metabolic processes on proteins and enzymatic conversions through a surge of
  • post WWII research that gave birth to centers for basic science research in biology and medicine in both US and in England, which was preceded by work in prewar Germany. This is to be followed by further developments related to the Human Genome Project.
  • Transcription initiation (Photo credit: Wikipedia)
  • Schematic relationship between biochemistry, genetics, and molecular biology (Photo credit: Wikipedia)
  • Central dogma of molecular biology (Photo credit: Wikipedia)


Transcription initiation

Transcription initiation (Photo credit: Wikipedia)

Schematic relationship between biochemistry, g...

Schematic relationship between biochemistry, genetics, and molecular biology (Photo credit: Wikipedia)

Central dogma of molecular biology

Central dogma of molecular biology (Photo credit: Wikipedia)








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