Genetic Recombination in Bacillus subtilis 168: Effect of DhelD on DNA Repair and Homologous Recombination

The B. subtilis DhelD allele rendered cells proficient in transformational recombination and moderately sensitive to methyl methanesulfonate when present in an otherwise Rec strain. The DhelD allele was introduced into rec-deficient strains representative of the a (recF strain), b (addA addB), g (recH), « (DrecU), and z (DrecS) epistatic groups. The DhelD mutation increased the sensitivity to DNA-damaging agents of addAB, DrecU, and DrecS cells, did not affect the survival of recH cells, and decreased the sensitivity of recF cells. DhelD also partially suppressed the DNA repair phenotype of other mutations classified within the a epistatic group, namely the recL, DrecO, and recR mutations. The DhelD allele marginally reduced plasmid transformation (threeto sevenfold) of mutations classified within the a, b, and g epistatic groups. Altogether, these data indicate that the loss of helicase IV might stabilize recombination repair intermediates formed in the absence of recFLOR and render recFLOR, addAB, and recH cells impaired in plasmid transformation.