title: Bacterial genes mutL, mutS, and dcm participate in repair of mismatches at 5-methylcytosine sites.
abstract: Certain amber mutations in the cI gene of bacteriophage lambda appear to recombine very frequently with nearby mutations. The aberrant mutations included C-to-T transitions at the second cytosine in 5'CC(A/T)GG sequences (which are subject to methylation by bacterial cytosine methylase) and in 5'CCAG and 5'CAGG sequences. Excess cI+ recombinants arising in crosses that utilize these mutations are attributable to the correction of mismatches by a bacterial very-short-patch (VSP) mismatch repair system. In the present study I found that two genes required for methyladenine-directed (long-patch) mismatch repair, mutL and mutS, also functioned in VSP mismatch repair; mutH and mutU (uvrD) were dispensable. VSP mismatch repair was greatly reduced in a dcm Escherichia coli mutant, in which 5-methylcytosine was not methylated. However, mismatches in heteroduplexes prepared from lambda DNA lacking 5-methylcytosine were repaired in dcm+ bacteria. These results indicate that the product of gene dcm has a repair function in addition to its methylase activity.
mesh_terms: D044503:5-Methylcytosine; D010582:Bacteriophage lambda / Q000235:genetics*; D001483:Base Sequence; D003596:Cytosine / Q000031:analogs & derivatives; D004249:DNA Damage; D004260:DNA Repair; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics*; D005798:Genes, Bacterial; D005814:Genes, Viral; D009154:Mutation; D009692:Nucleic Acid Heteroduplexes
chemical_list: D004269:DNA, Bacterial; D009692:Nucleic Acid Heteroduplexes; D044503:5-Methylcytosine; D003596:Cytosine