Genetic recombination in Bacillus subtilis 168: Effect of Delta helD on DNA repair and homologous recombination

The B. subtilis Delta helD allele rendered cells proficient in transformati onal recombination and moderately sensitive to methyl methanesulfonate when present in an otherwise Rec(+) strain. The Delta helD allele was introduce d into rec-deficient strains representative of the alpha (recF strain), bet a (addA addB), gamma (recH), kappa (Delta recU), and zeta (Delta recS) epis tatic groups. The Delta helD mutation increased the sensitivity to DNA-dama ging agents of addAB, Delta recU, and Delta recS cells, did not affect the survival of recH cells, and decreased the sensitivity of recF cells. Delta helD also partially suppressed the DNA repair phenotype of other mutations classified within the alpha epistatic group, namely the recL, Delta recO, a nd recR mutations. The Delta helD allele marginally reduced plasmid transfo rmation (three- to sevenfold) of mutations classified within the alpha, bet a, and gamma epistatic groups. Altogether, these data indicate that the los s of helicase IV might stabilize recombination repair intermediates formed in the absence of recFLOR and render recFLOR, addAB, and recH cells impaire d in plasmid transformation.