The nuclease activities of both the S mr domain and an additional LDLK motif are required for an efficient anti‐recombination function of H elicobacter pylori MutS2

Summary H elicobacter pylori , a human pathogen, is a naturally and constitutively competent bacteria, displaying a high rate of intergenomic recombination. While recombination events are essential for evolution and adaptation of H . pylori to dynamic gastric niches and new hosts, such events should be regulated tightly to maintain genomic integrity. Here, we analyze the role of the nuclease activity of MutS2 , a protein that limits recombination during transformation in H . pylori . In previously studied MutS2 proteins, the C ‐terminal S mr domain was mapped as the region responsible for its nuclease activity. We report here that deletion of S mr domain does not completely abolish the nuclease activity of HpMutS2 . Using bioinformatics analysis and mutagenesis, we identified an additional and novel nuclease motif ( LDLK ) at the N ‐terminus of HpMutS2 unique to H elicobacter and related ε‐proteobacterial species. A single point mutation ( D30A ) in the LDLK motif and the deletion of S mr domain resulted in ∼ 5–10‐fold loss of DNA cleavage ability of HpMutS2 . Interestingly, the mutant forms of HpMutS2 wherein the LDLK motif was mutated or the S mr domain was deleted were unable to complement the hyper‐recombination phenotype of a mutS2 − strain, suggesting that both nuclease sites are indispensable for an efficient anti‐recombinase activity of HpMutS2 .