Christopher W. Lawrence, Ph.D.

Our work is concerned with investigating DNA-damage induced mutagenesis, and the replication of damaged DNA which gives rise to these mutations, in budding yeast and E. coli. Such replication is used when unrepaired damage delays the progress of replication forks, and depends on a set of proteins at least partly different from those needed for replication on undamaged templates. Although only a minor cellular mechanism for coping with DNA damage, it is a major source of mutations. Understanding this process may therefore provide novel strategies for preventing cancer, since mutations commonly contribute to the development of this disease. To this end, we have cloned and sequenced yeast genes concerned with mutagenesis and, in collaboration with David Hinkle (Biology Department) examined the enzymatic properties of their purified products. In particular, we are investigating the properties of a new DNA polymerase, Pol zeta, a complex formed by the products of the REV3 and REV7 genes. The sole function of Pol zeta appears to be replication past damage sites in the DNA template, which it performs more efficiently than the major replicases. We are also investigating the properties of the REV1 gene product, which possesses a novel deoxycytidyl transferase activity that is required for replication past abasic lesions.

Studies with E. coli. carried out in collaboration with Roger Woodgate (NIH) and Myron Goodman (USC), are concerned with understanding the in vivo functions of the UmuD'C protein complex, which plays a crucial role in replication past DNA damage in this organism. In particular, we are attempting to identify the DNA polymerase holoenzyme subunits with which the complex interacts, and to determine the relative roles of DNA polymerase II and III. These questions are being investigated by transforming different mutant strains with single stranded vectors that carry a specified mutagenic lesion at a defined site. Such vectors are powerful tools for this purpose because they provide direct and independent estimates of the frequency of replication past the lesion and of the frequency with which mutations are induced by this process.