Replication restart in Escherichia coli: Genetic studies at the interface of recombination and replication
DNA replication forks are frequently detained during their progression from oriC to the replication terminus due to encounters with DNA lesions or proteins blocking the way. For survival, cells deploy a number of enzymes catalyzing replication restart at or near the damaged site. The preprimosomal protein, PriA, along with several accessory proteins, directs DnaB helicase to the lagging-strand template during assembly of the replisome. This helicase loading mechanism is analogous to that catalyzed by DnaA at oriC, except that PriA-directed fork assembly does not require oriC or any specific initiation sequence. Instead, it recognizes and binds with high specificity to various recombinational intermediates such as D loops that form during the recombination-mediated repair of replication forks. In this manner, PriA effectively links the processes of homologous recombination and DNA replication. PriA also possesses a 3′ to 5′ helicase activity that might be important for restarting stalled forks directly in the absence of homologous recombination. This lab uses a genetic approach to understand the in vivo functions of PriA and its accessory proteins, PriB, PriC, DnaT, DnaC, and Rep. Extensive phenotypic analyses of mutants of priA, priB, priC, dnaC and rep have clearly indicated that replication restart occurs by multiple pathways (Sandler 2000). The work presented in this dissertation continues to explore and test the multiple pathways model for replication restart. Three lines of investigation were pursued: (1) Can genetic evidence support a role for dnaT in replication restart? If so, then for which pathway(s) is dnaT important? (2) It has been proposed that priA mutants accumulate recombinational intermediates. Can this be detected in individual cells using a DNA stain to examine nucleoid organization? (3) PriA mutants are chronically SOS induced. Microscopy indicates that two kinds of cells are present in log phase cultures. Are SOS genes turned on in both populations of cells or only in a subpopulation?
0307: Molecular biology