Our objective is to understand the molecular mechanisms responsible for misrepair mutagenesis in Escherichia coli. These processes are elicited in response to DNA damage inflicted by a variety of mutagens, both physical and chemical, that occur in our environment naturally or are produced by human activity. These agents not only cause mutations, but, by altering certain regulatory genes, may also play a role in carcinogenesis. Such mutagens are a potential health hazard, therefore, though the extent to which this potential for harm is realized is not yet clear in many cases. Direct measurement of hazard at the low levels of damage usually encountered is rarely feasible, and extrapolation from experimental results with high doses of mutagen administered to non-human organisms is hampered by lack of information about the relevant mechanisms. Work in this project should help to provide such information. Our specific goals are to determine the types and frequencies of mutations induced by specific DNA lesions, namely, cyclobutane bipyrimidines and 6,4 Pyo adducts; to obtain evidence in vivo and in vitro for bypass replication, the process thought to cause mutations, and to see if the mechanisms for bypass replication differ when single- as opposed to double-stranded DNA is replicated; to investigate the properties of the umuDC gene, which is thought to play an important role in bypass replication; and to investigate the phenomenon of untargeted mutagenesis as a means of gaining insight into changes in the replication complex that result from UV irradiation. We will use a combination of genetical and molecular biological techniques to achieve these aims, including the sequencing of induced mutations, the construction of synthetic oligonucleotide hybrid phages containing a single defined lesion at a specific site, and the development of an in vitro system with which to study bypass replication.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
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Microbial Physiology and Genetics Subcommittee 2 (MBC)
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University of Rochester
School of Medicine & Dentistry
United States
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Ozgenc, Ali I; Szekeres, Edward S; Lawrence, Christopher W (2005) In vivo evidence for a recA-independent recombination process in Escherichia coli that permits completion of replication of DNA containing UV damage in both strands. J Bacteriol 187:1974-84
Borden, Angela; O'Grady, Paul I; Vandewiele, Dominique et al. (2002) Escherichia coli DNA polymerase III can replicate efficiently past a T-T cis-syn cyclobutane dimer if DNA polymerase V and the 3' to 5' exonuclease proofreading function encoded by dnaQ are inactivated. J Bacteriol 184:2674-81
Vandewiele, D; Borden, A; O'Grady, P I et al. (1998) Efficient translesion replication in the absence of Escherichia coli Umu proteins and 3'-5' exonuclease proofreading function. Proc Natl Acad Sci U S A 95:15519-24
Horsfall, M J; Borden, A; Lawrence, C W (1997) Mutagenic properties of the T-C cyclobutane dimer. J Bacteriol 179:2835-9
Gentil, A; Le Page, F; Margot, A et al. (1996) Mutagenicity of a unique thymine-thymine dimer or thymine-thymine pyrimidine pyrimidone (6-4) photoproduct in mammalian cells. Nucleic Acids Res 24:1837-40
Lawrence, C W; Hinkle, D C (1996) DNA polymerase zeta and the control of DNA damage induced mutagenesis in eukaryotes. Cancer Surv 28:21-31
Szekeres Jr, E S; Woodgate, R; Lawrence, C W (1996) Substitution of mucAB or rumAB for umuDC alters the relative frequencies of the two classes of mutations induced by a site-specific T-T cyclobutane dimer and the efficiency of translesion DNA synthesis. J Bacteriol 178:2559-63
Lawrence, C W; Borden, A; Woodgate, R (1996) Analysis of the mutagenic properties of the UmuDC, MucAB and RumAB proteins, using a site-specific abasic lesion. Mol Gen Genet 251:493-8
Horsfall, M J; Lawrence, C W (1994) Accuracy of replication past the T-C (6-4) adduct. J Mol Biol 235:465-71
Lawrence, C W; Gibbs, P E; Borden, A et al. (1993) Mutagenesis induced by single UV photoproducts in E. coli and yeast. Mutat Res 299:157-63

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