Genetic Recombination inBacillus subtilis168: Contribution of Holliday Junction Processing Functions in Chromosome Segregation

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Abstract
Bacillus subtilis mutants classified within the ε (ruvA, ΔruvB, ΔrecU, and recD) and η (ΔrecG) epistatic groups, in an otherwise rec+ background, render cells impaired in chromosomal segregation. A less-pronounced segregation defect in ΔrecA and Δsms (ΔradA) cells was observed. The repair deficiency of addAB, ΔrecO, ΔrecR, recH, ΔrecS, and ΔsubA cells did not correlate with a chromosomal segregation defect. The sensitivity of ε epistatic group mutants to DNA-damaging agents correlates with ongoing DNA replication at the time of exposure to the agents. The Δsms (ΔradA) and ΔsubA mutations partially suppress the DNA repair defect in ruvA and recD cells and the segregation defect in ruvA and ΔrecG cells. The Δsms (ΔradA) and ΔsubA mutations partially suppress the DNA repair defect of ΔrecU cells but do not suppress the segregation defect in these cells. The ΔrecA mutation suppresses the segregation defect but does not suppress the DNA repair defect in ΔrecU cells. These results result suggest that (i) the RuvAB and RecG branch migrating DNA helicases, the RecU Holliday junction (HJ) resolvase, and RecD bias HJ resolution towards noncrossovers and that (ii) Sms (RadA) and SubA proteins might play a role in the stabilization and or processing of HJ intermediates.