The mmsA locus of Streptococcus pneumoniae encodes a RecG‐like protein involved in DNA repair and in three‐strand recombination

Abstract

We describe the characterization of a mutant strain of Streptococcus pneumoniae previously isolated on the basis of its sensitivity to Methyl Methane Sulphonate (MMS). The mutant strain also exhibited increased sensitivity to UV light and to X-rays, together with a reduced capacity for recombination and Hex-mediated generalized mismatch repair. We show that the original mutant contains two unlinked mutations in the mmsA and in the pms genes. The mmsA wild-type region was cloned and the nucleotide sequence of the mmsA gene was determined. mmsA encodes a polypeptide of 671 amino acids related to a large family of DNA-RNA helicases, with the highest similarity to Escherichia coli RecG, a protein involved in the branch migration of Holliday junctions. A plasmid carrying the intact mmsA coding region was shown to restore UV resistance to E. coli recG mutant strains. An mmsA-null mutant constructed by insertion of a chloramphenicol-resistance gene exhibited a 25-fold reduction in recombination during transformation. We suggest that MmsA recognizes and branch migrates three-strand transformation intermediates to extend donor-recipient heteroduplex regions. The mmsA-null mutant exhibited the other phenotypes of the original mutant, apart from mismatch-repair deficiency and, in addition, an alteration in colony-forming ability was noticed. In the pms mutant background, all phenotypes caused by the mmsA mutation were attenuated. Therefore, the pms mutation, although it affected mismatch repair and, to some extent, DNA repair and recombination, acted as a suppressor of the mmsA mutation.

Effect of Host Species on RecG Phenotypes in Helicobacter pylori and Escherichia coli

“…In previous studies of S. aureus, Streptococcus pneumoniae, and E. coli, RecG has been important in recovery after exposure to DNA-damaging agents (34,41,48), whereas our studies indicate that RecG is not involved in DNA repair in H. pylori after damage due to exposure to UV (Fig. 4) or methyl methanesulfonate (data not shown).…”

“…Cross-species complementation studies performed between E. coli and H. pylori suggest that their RecG proteins are functionally interchangeable in E. coli but display phenotypic differences reflecting divergent intracellular environments. Unlike other RecG homologs (34,41,48), the H. pylori RecG (encoded by hp1523), is not required for recovery from DNA damage, although it plays a role in limiting recombination. These findings suggest that HP1523, influencing genomic plasticity in H. pylori without involvement in DNA repair pathways, functions in a new role for RecG helicase homologs.…”

Helicobacter pylori Mutants Defective in RuvC Holliday Junction Resolvase Display Reduced Macrophage Survival and Spontaneous Clearance from the Murine Gastric Mucosa

“…This disparity may reflect differences in the repertoire of recombination enzymes available in H. pylori or may be due to unique features of DNA processing during natural transformation. A similarly severe defect in transformation has also been observed with Streptococcus pneumoniae recG mutants, while the corresponding mutants in E. coli are relatively proficient at recombination (31). Given that RecG also participates in processing branched intermediates and displays a significant functional overlap with RuvABC (27), examination of the relative contribution of both pathways to H. pylori transformation and DNA repair merits investigation.…”

Characterization of In Vitro Biofilm-Associated Pneumococcal Phase Variants of a Clinically Relevant Serotype 3 Clone

“…Since phase variants can arise through point mutations (12), it is plausible that phase variation is partially regulated by mismatch repair genes. In S. pneumoniae, the mismatch repair genes include the Hex genes (11,15) and the Hex-independent genes, the mutY and mutX genes (8,25,30), and the pms gene (22). The rough phase variants with deletions, which have not previously been described in a biofilm model, did not appear to arise through recombinational events of nontandem repeats (28).…”