HOMOLOGOUS RECOMBINATION-DEPENDENT INITIATION OF DNA-REPLICATION FROM DNA DAMAGE-INDUCIBLE ORIGINS IN ESCHERICHIA-COLI

Escherichia coli cells induced for the SOS response express inducible stable DNA replication (iSDR) as an SOS function. Initiation of iSDR is independent of transcription, translation and DnaA protein, which are essential for initiation of DNA replication from oriC. We found that a recA mutant that is defective in recombination but proficient in SOS induction could not elicit iSDR. In contrast, iSDR was enhanced by recD and recJ mutations that inactivate the exonuclease V activity of the RecBCD enzyme and the RecJ exonuclease activity, respectively. A mutation in the ruvC gene that blocks the resolution of recombination intermediates (i.e. Holliday structures) also enhanced iSDR. Furthermore, inhibition of branch migration by recG or ruvAB mutations dramatically increased the iSDR activity. recBC mutants are defective in iSDR induction but the defect was suppressed by a mutation in the sbcA gene. The major product of minichromosomes replicated by iSDR was covalently closed circular monomers. We propose that recombination intermediates (i.e. D-loop structures) created by the action of RecA recombinase and RecBC(D) helicase play a central role in initiation of iSDR.