RECF AND RECR ARE REQUIRED FOR THE RESUMPTION OF REPLICATION AT DNA-REPLICATION FORKS IN ESCHERICHIA-COLI

Escherichia coli containing a mutation in recF are hypersensitive to U V. However, they exhibit normal levels of conjugational or transductio nal recombination unless the major pathway (recBC) is defective. This implies that the UV sensitivity of recF mutants is not due to a defect in recombination such as occurs during conjugation or transduction. H ere, we show that when replication is disrupted, at least two genes in the recF pathway, recF and recR, are required for the resumption of r eplication at DNA replication forks, and that in their absence, locali zed degradation occurs at the replication forks. Our observations supp ort a model in which recF and recR are required to reassemble a replic ation holoenzyme at the site of a DNA replication fork. These results, when taken together with previous literature, suggest that the UV hyp ersensitivity of recF cells is due to an inability to resume replicati on at disrupted replication forks rather than to a defect in recombina tion. Current biochemical and genetic data on the conditions under whi ch recF-mediated recombination occurs suggest that the recombinational intermediate also may mimic the structure of a disrupted replication fork.