Preferential post-replication repair of DNA lesions situated on the leading strand of plasmids in Escherichia coli

Abstract

In Escherichia coli, RecF-dependent post-replication repair (PRR) permits cells to tolerate the potentially lethal effects of blocking lesions at the replication fork. We have developed an in vivo experimental system to study the PRR mechanisms that allow blocked replication forks to be rescued by homologous sequences. We show that approximately 80% of the PRR events observed in SOS-uninduced cells are generated by RecA-mediated excision repair, a novel nucleotide excision repair- and RecA/RecF-dependent mechanism, while 20% are generated by RecF-dependent homologous recombination. Moreover, we show that in a wild-type background, PRR is approximately an order of magnitude more efficient in processing DNA containing a blocked leading strand, as compared with a blocked lagging strand. This strand bias is abolished in cells that are deficient in nucleotide excision repair. These results are discussed in the context of recent models describing the mechanisms of replication past damaged templates. © 2008 The Authors.