title: DNA sequence analysis of mutagenicity and site specificity of ethyl methanesulfonate in Uvr+ and UvrB- strains of Escherichia coli.
abstract: EMS-induced mutations within a 180 base pair region of the lacI gene of E. coli were cloned and sequenced. In total, 105 and 79 EMS-induced mutations from a Uvr+ and a UvrB- strain, respectively, were sequenced. The specificity of EMS-induced mutagenesis was very similar in the two strains; G:C----A:T transitions accounted for all but three of the mutants. The overall frequency of induced mutation was fivefold higher in the UvrB- strain compared to the Uvr+ strain. This demonstrates, at the DNA sequence level, that the presumed premutagenic lesion, O6-ethylguanine, is subject to repair by the uvrABC excision repair system of E. coli. An analysis of mutation frequencies with respect to neighboring base sequence, in the two strains, shows that O6-ethylguanine lesions adjacent to A:T base pairs present better targets for the excision repair machinery than those not adjacent to A:T base pairs.
mesh_terms: D001483:Base Sequence; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000235:genetics*; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics* / Q000528:radiation effects; D005020:Ethyl Methanesulfonate / Q000494:pharmacology*; D005798:Genes, Bacterial / Q000187:drug effects*; D009154:Mutation; D013045:Species Specificity; D014466:Ultraviolet Rays
chemical_list: D004269:DNA, Bacterial; D005020:Ethyl Methanesulfonate