title: DNA mismatch-repair in Escherichia coli counteracting the hydrolytic deamination of 5-methyl-cytosine residues.
abstract: Derivatives of phage M13 were constructed and used for the in vitro preparation of heteroduplex DNA molecules containing base/base mismatches that mimick DNA lesions caused by hydrolytic deamination of 5-meC residues in Escherichia coli DNA (i.e. they carry a T/G mismatch in the special sequence context provided by the recognition site -CCA/TGG-of the Dcm-methyltransferase). Upon introduction of these heteroduplex DNAs into CaCl2-treated E. coli cells, the mismatches are efficiently repaired with high bias in favour of the DNA strand containing the mismatched guanine residue. This special DNA mismatch-repair operates on fully dam-methylated DNA and is independent of gene mutH. It thus fulfills the salient requirements of a repair pathway responsible for counteracting the spontaneous hydrolytic deamination of 5-meC in vivo. The repair efficiency is boosted by a 5-methyl group present on the cytosine residue at the next-nearest position to the 5' side of the mismatched guanine. The repair is severely impaired in host strains carrying a mutation in any of the three loci dcm, mutL and mutS.
mesh_terms: D044503:5-Methylcytosine; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D003090:Coliphages / Q000235:genetics; D003596:Cytosine / Q000031:analogs & derivatives*; D004260:DNA Repair; D004926:Escherichia coli / Q000235:genetics*; D005796:Genes; D005798:Genes, Bacterial; D006868:Hydrolysis; D009154:Mutation
chemical_list: D001426:Bacterial Proteins; D044503:5-Methylcytosine; D003596:Cytosine