Characterization of Biochemical Properties of Bacillus subtilis RecQ Helicase

RecQ family helicases function as safeguards of the genome. UnlikeEscherichia coli , the Gram-positiveBacillus subtilis bacterium possesses two RecQ-like homologues, RecQ[Bs] and RecS, which are required for the repair of DNA double-strand breaks. RecQ[Bs] also binds to the forked DNA to ensure a smooth progression of the cell cycle. Here we present the first biochemical analysis of recombinant RecQ[Bs]. RecQ[Bs] binds weakly to single-stranded DNA (ssDNA) and blunt-ended double-stranded DNA (dsDNA) but strongly to forked dsDNA. The protein exhibits a DNA-stimulated ATPase activity and ATP- and Mg2+ -dependent DNA helicase activity with a 3′→5′ polarity. Molecular modeling shows that RecQ[Bs] shares high sequence and structure similarity withE. coli RecQ. Surprisingly, RecQ[Bs] resembles the truncatedSaccharomyces cerevisiae Sgs1 and human RecQ helicases more than RecQ[Ec] with regard to its enzymatic activities. Specifically, RecQ[Bs] unwinds forked dsDNA and DNA duplexes with a 3′-overhang but is inactive on blunt-ended dsDNA and 5′-overhung duplexes. Interestingly, RecQ[Bs] unwinds blunt-ended DNA with structural features, including nicks, gaps, 5′-flaps, Kappa joints, synthetic replication forks, and Holliday junctions. We discuss these findings in the context of RecQ[Bs]'s possible functions in preserving genomic stability.