Effect of the recU suppressors sms and subA on DNA repair and homologous recombination in Bacillus subtilis

Abstract.

In Bacillus subtilis, mutant alleles of the genes sms and subA partially suppress the recombination phenotype of recU cells. When present in an otherwise Rec⁺ strain, Δsms and ΔsubA alleles render cells slightly sensitive to DNA-damaging agents, and impair chromosomal transformation (3- to 10-fold reduction), but do not affect plasmid transformation (less than 1.5-fold reduction). The Δsms and ΔsubA alleles were introduced into rec-deficient strains representative of the epistatic groups α (recF strain), β (addA addB), γ (recH), ε (recB, ΔrecU and recD strains) and ζ (ΔrecS). Both the Δsms and ΔsubA mutations were found to increase sensitivity to DNA-damaging agents in recF, ΔrecS and addAB cells. In contrast, the Δsms mutations decreased the sensitivity of recB, ΔrecU, recD and recH cells, and the ΔsubA mutation decreased the sensitivity of recB and ΔrecU cells to DNA-damaging agents. Functions classified within the epistatic groups α, ε and ζ are required for intramolecular recombination, measured as plasmid transformation. The Δsms and ΔsubA mutations, which partially suppressed the recombinational repair phenotype of mutants for functions within epistatic group ε, enhanced plasmid transformation of recU (recB, recD) and recS cells by 10- to 20-fold. In the absence of the proteins Sms and SubA, the recombination machinery is apparently redirected towards (an) alternative pathway(s). Furthermore, the shared ability of the Δsms and ΔsubA mutations to act as indirect suppressors of recB, recU and recD mutations supports the classification of the recBUD genes within epistatic group ε.