Genetic Recombination in Bacillus subtilis 168: Contribution of Holliday Junction Processing Functions in Chromosome Segregation

Abstract

ABSTRACT Bacillus subtilis mutants classified within the ε ( ruvA , Δ ruvB , Δ recU , and recD ) and η (Δ recG ) epistatic groups, in an otherwise rec + background, render cells impaired in chromosomal segregation. A less-pronounced segregation defect in Δ recA and Δ sms (Δ radA ) cells was observed. The repair deficiency of addAB , Δ recO , Δ recR , recH , Δ recS , and Δ subA 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 Δ sms (Δ radA ) and Δ subA mutations partially suppress the DNA repair defect in ruvA and recD cells and the segregation defect in ruvA and Δ recG cells. The Δ sms (Δ radA ) and Δ subA mutations partially suppress the DNA repair defect of Δ recU cells but do not suppress the segregation defect in these cells. The Δ recA mutation suppresses the segregation defect but does not suppress the DNA repair defect in Δ recU 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.