The RuvAB branch migration translocase and RecU Holliday junction resolvase are required for double-stranded DNA break repair in Bacillus subtilis

In models of Escherichia coli recombination and DNA repair, the RuvABC complex directs the branch migration and resolution of Holliday junction DNA. To probe the validity of the E. coli paradigm, we examined the impact of mutations in ruvAB and recU (a ruvC functional analog) on DNA repair. Under standard transformation conditions we failed to construct ruvAB recG, recU ruvAB, recU recG, or recU recJ strains. However, ruvAB could be combined with addAB (recBCD), recF, recH, recS, recQ, and recJ mutations. The ruvAB and recU mutations rendered cells extremely sensitive to DNA-damaging agents, although less sensitive than a recA strain. When damaged cells were analyzed, we found that RecU was recruited to defined double-stranded DNA breaks (DSBs) and colocalized with RecN. RecU localized to these centers at a later time point during DSB repair, and formation was dependent on RuvAB. In addition, expression of RecU in an E. coli ruvC mutant restored full resistance to UV light only when the ruvAB genes were present. The results demonstrate that, as with E. coli RuvABC, RuvAB targets RecU to recombination intermediates and that all three proteins are required for repair of DSBs arising from lesions in chromosomal DNA