Role for DNA double strand end-resection activity of RecBCD in control of aberrant chromosomal replication initiation in Escherichia coli

Replication of the circular bacterial chromosome is initiated from a locus oriC with the aid of an essential protein DnaA. One approach to identify factors acting to prevent aberrant oriC-independent replication initiation in Escherichia coli has been that to obtain mutants which survive loss of DnaA. Here we show that a {Delta}recD mutation, associated with attenuation of RecBCDs DNA double strand end-resection activity, provokes abnormal replication and rescues {Delta}dnaA lethality in two situations: (i) in absence of 5-3 single-strand DNA exonuclease RecJ, or (ii) when multiple two-ended DNA double strand breaks (DSBs) are generated either by I-SceI endonucleolytic cleavages or by radiomimetic agents phleomycin or bleomycin. One-ended DSBs in the {Delta}recD mutant did not rescue {Delta}dnaA lethality. With two-ended DSBs in the {Delta}recD strain, {Delta}dnaA viability was retained even after linearization of the chromosome. Data from genome-wide DNA copy number determinations in {Delta}dnaA-rescued cells lead us to propose a model that nuclease-mediated DNA resection activity of RecBCD is critical for prevention of a {sigma}-mode of rolling-circle over-replication when convergent replication forks merge and fuse, as may be expected to occur during normal replication at the chromosomal terminus region or during repair of two-ended DSBs following "ends-in" replication.