REQUIREMENT OF RECBC ENZYME AND AN ELEVATED LEVEL OF ACTIVATED RECA FOR INDUCED STABLE DNA-REPLICATION IN ESCHERICHIA-COLI

During SOS induction, Escherichia coli cells acquire the ability to replicate DNA in the absence of protein synthesis, i.e., induces stable DNA replication (iSDR). Initiation of iSDR can occur in the absence of transcription and DnaA protein activity, which are both required for initiation of normal DNA replication at the origin of replication, oriC. In this study we examined the requirement or recB, recC, and recA for the induction and maintenance of iSDR. We found that recB and recC mutations blocked the induction of iSDR by UV radiation and nalidixic acid treatment. In recB(Ts) strains, iSDR activity induced at 30°C was inhibited by subsequent incubation at 42°C. In addition, iSDR that was induced after heat activation of the RecA441 protein was abolished by the recB21 mutation. These results indicated that the RecBC enzyme was essential not only for SOS signal generation but also for the reinitiation of DNA synthesis following DNA damage. recAo(Con) lexA3(Ind-) strains were found to be capable of iSDR after nalidixic acid treatment, indicating that the derepression of the recA gene and the activation of the elevated level of RecA protein were the necessary and sufficient conditions for the induction of iSDR.