Molecular genetics; Protein Function and Structure; DNA Replication, Recombination and Repair; Bacterial Pathogenesis
My associates and I use a combination of biochemical and biophysical approaches to study the molecular basis of stalled DNA replication fork rescue. Our model organism is the well-characterized bacterium Escherichia coli (E. coli), since the majority of the proteins thought to be involved in fork rescue are known. Most of our experimental work is concerned with the function and regulation of the complexes that control fork rescue, with studies focused primarily on the role of the single-strand DNA binding protein (SSB) and several recombination DNA helicases. Comparative studies are also underway using selected components of some medically relevant bacterial organisms. We collaborate with scientists from the National Institutes of Health (NIH) and other research institutions. The team working in my lab consists of undergraduate and graduate students, postdoctoral fellows and a technician. We seek to understand fork rescue utilizing both bulk-phase and single molecule techniques. Typically, studies focus initially on purification and characterization of the various proteins (there are now more than 10 being studied). We study DNA binding, unwinding and the hydrolysis of adenosine triphosphate (ATP) using a combination of modern spectroscopic (both ultraviolet–visible and fluorescence) and equilibrium binding methods. The goal of these initial studies is to understand the range of DNA substrates on which an enzyme can act, as a means to understanding its role in vivo. This is followed by careful single molecule studies using a technique I pioneered that combines optical tweezers, microfluidics and high-resolution fluorescence microscopy. My research team is also pursuing a new area of research targeted at developing small molecule inhibitors. These are aimed at disrupting binding between SSB and the 12-14 proteins comprising the SSB-interactome. As SSB is an essential protein and its binding to interactome partners is required for viability, the goal of these studies is to identify inhibitors that will be further developed into novel antibiotics.
Infectious Disease; Microbiology; Molecular and Cellular Biology; Molecular genetics; DNA Replication, Recombination and Repair; Virology; Genome Integrity
The major focus of my laboratory is in understanding the molecular machines that make up the DNA replication forks of the small human DNA viruses, polyoma- and papillomaviruses. Papillomaviruses and polyomaviruses are human pathogens; human papillomavirus (HPV) results in a vast number of human cancers, and the human polyomaviruses JC and BK cause serious disease and death in immunocompromised patients. Both viral systems provide important models for the study of human DNA replication mechanisms and have allowed for vital insights into eukaryotic DNA replication. The study of polyomavirus DNA replication led to the first identification of many cellular DNA replication complexes and processes; papillomavirus has provided the best structures and models to date of replicative hexameric DNA helicases and how they function. I typically train undergraduate, master’s and doctoral students and postdoctoral scholars, assistant research professors and laboratory technicians. My laboratory focuses on two primary areas. One is elucidating the dynamic protein-protein interactions that allow the series of enzymes required to replicate DNA to act in concert and in the correct sequence required to duplicate the genome. My laboratory has been at the forefront of identifying the interactions between the one critical HPV DNA replication protein, the origin-binding DNA helicase, E1, and cellular DNA replication proteins. Understanding these interactions and the roles they play in the HPV DNA replication process has helped our understanding of, and continues to lead to information that tells us more about how both viral and eukaryotic DNA replication forks function. In addition, as we identify protein-protein interactions between HPV E1 and cellular factors that are essential for HPV DNA synthesis, we will uncover potential targets for development of broad-range HPV antivirals that could act to block HPV replication. We recently obtained a large multilaboratory NIH research grant to investigate just this possibility for the interaction between HPV E1 and the human DNA replication protein, Topoisomerase I. The second primary area of investigation is elucidating how the cellular DNA damage response (DDR) pathways inhibit DNA replication when cells are subjected to DNA damage. For many years, the DDR field focused on the effects of DDR on the cell cycle kinases as the only method by which DNA replication was arrested. In the mid- to late-2000s, researchers recognized that in mammalian cells there is also a substantial (tenfold) inhibition of elongation of DNA replication following DDR. The mechanisms for this inhibition are unknown. Using both in vitro and cell-based simian virus 40 (SV40) DNA replication systems, we have shown that SV40 DNA replication is also shut down in response to DDR kinase pathways and that this is not based on cell cycle kinase action. Therefore, SV40 provides a useful model system for determining how elongation of DNA replication is inhibited by DDR. Furthermore, we have shown that in contrast HPV DNA replication does not respond to DDR, providing us an important control DNA replication system for these studies. (The lack of DDR arrest of HPV DNA replication likely explains why HPV integrates so readily into host cell chromosomes−an important step for HPV-induced carcinogenesis). Our studies on the DDR effect on polyoma and papilloma virus DNA replication will lead to insights into the effect of DDR on cellular DNA replication as well as an understanding of how HPV integrates into host cell chromosomes causing HPV-induced cancers.
Cell growth, differentiation and development; DNA Replication, Recombination and Repair; Gene Expression; Molecular and Cellular Biology; Proteins and metalloenzymes; Signal Transduction; Transcription and Translation
The main goal of my research group is to understand the role of N-terminal methylation on human development and disease. I identified the first eukaryotic N-terminal methyltransferases, NRMT1 and NRMT2, and am now working to identify how these enzymes and this new type of methylation affect cancer development and ageing. Our laboratory has shown that NRMT1 functions as a tumor suppressor in mammary glands, and its loss sensitizes breast cancer cells to DNA damaging chemotherapeutics. We have also created the first NRMT1 knockout mouse and shown it to have developmental defects, as well as, exhibit phenotypes of premature ageing. Currently, we are working to understand the exact biochemical pathways that lead from loss of N-terminal methylation to these phenotypes. We are also studying how post-translational modifications on the N-terminus of proteins may interact and dictate protein function, similar to the post-translational modifications found on histone tails.
DNA Replication, Recombination and Repair; Genome Integrity; Molecular and Cellular Biology; Molecular genetics; Protein Function and Structure
In my laboratory, we are interested in the general problem of maintaining genome stability. To this end, we focus on two distinct aspects of genome stability: 1) the roles of mismatch (MMR) proteins in multiple pathways for DNA repair and 2) the manner in which regulation of dNTP pools, through the regulation of ribonucleotide reductase (RNR) activity, impacts genome integrity. 1) MMR proteins recognize many different types of DNA lesions and then target the lesion for the appropriate repair pathway. We are interested in the mechanism(s) by which recognition of a lesion is translated into the appropriate DNA repair pathway, using the yeast Saccharomyces cerevisiae as a model system. Is it through differential protein-nucleic acid or protein-protein interactions? To address these questions as well as the regulation of DNA repair pathway selection, we use a combination of genetic, biochemical and biophysical approaches. 2) RNR activity modulates the level of dNTPs that are available in a cell at a given time. Higher levels of dNTPs lead to higher mutation rates. We are interested in the various ways in which misregulated dNTP pools might affect cellular metabolism and affect the stability of the genome.
DNA Replication, Recombination and Repair; Gene Expression; Genome Integrity; Microbiology; Molecular and Cellular Biology; Protein Function and Structure; Signal Transduction
We are interested in developing an integrated mechanistic view of how organisms coordinate the actions of their DNA replication machinery with those of other cellular factors involved in DNA repair and damage tolerance. Failure to properly coordinate these functions leads to mutations, genome instability, and in extreme cases, cell death. We utilize a combination of biochemical, biophysical, and genetic approaches to investigate the molecular mechanisms of DNA replication, DNA repair, and error-prone DNA damage tolerance functions in Escherichia coli. The primary mechanism for damage tolerance involves direct bypass of damaged bases in the DNA. This process is inherently error-prone, and is the basis for most mutations. Current efforts are focused on understanding the mechanisms by which the actions of high fidelity and error-prone lesion bypass DNA polymerases are coordinated with each other, as well as other proteins involved in DNA metabolism. Our goal in this work is to develop methods that enable us to control the fidelity of DNA repair for therapeutic gain. We are also interested in understanding the mechanisms that contribute to DNA mutagenesis in the opportunistic human pathogen, P. aeruginosa. P. aeruginosa is a particular problem for individuals afflicted with cystic fibrosis. Persistent colonization of cystic fibrosis airways with P. aeruginosa serves as a major source of morbidity and mortality for these patients. The ability of P. aeruginosa to persist in the airways relies in part on its ability to adapt to the continuously changing environment within the diseased airways. We are particularly interested in determining the contribution of mutagenesis and DNA repair to adaptive mutations that contribute to clonal expansion and pathoadaptation of P. aeruginosa during colonization of cystic fibrosis airways.