A New DNA Repair System for N6-Hydroxylaminopurine and other Base Analogs

Suny At Albany, Albany NY

Investigators

Abstract

It has been shown that replication forks formed at the origin of replication in Escherichia coli are not likely to circumnavigate the chromosome and finish a round of synthesis during normal cell growth. Replication forks are apparently derailed by endogenous DNA damage, and these forks must be reactivated in order to ensure cell division and bacterial cell survival. Reactivation requires homologous recombination functions and a replication restart primosome. The nature of the lesions that are formed under normal growth conditions are not well defined and may be either base lesions or strand breaks. Preliminary data suggest a connection between purine nucleoside metabolism and a form of DNA repair that results in stalled replication forks. The purine analog hydroxylaminopurine (HAP) will be used to mimic the effects of mutations that disrupt a repair pathway in E. coli. It is suggested that the endogenous lesions that block replication forks in E. coli under normal growth conditions arise from purine analogs that are converted into nucleoside triphosphates and then incorporated into DNA by replicative polymerases. This hypothesis leads to many predictions and raises many questions. Is it possible to identify the specific mechanism for HAP-induced cell killing? Can HAP be used as a probe of the enzymatic processes that remove endogenous aberrant purine nucleotide triphosphates from the replication precursor pool? Is it possible to identify the nucleoside triphosphates in E. coli under normal growth conditions that trigger replication fork arrest and restart? In order to answer these questions all the genes involved in the formation of nucleoside triphosphates containing base analogues and the subsequent removal of these compounds from nucleoside and nucleotide pools and from DNA will be identified.