Spontaneous mutagenesis in Escherichia coli strains lacking 6-methyladenine residues in their DNA: an altered mutational spectrum in dam- mutants.
The mutational spectrum at the lacI locus in a dam-4 strain of Escherichia coli was examined. The observed 20-fold increase in spontaneous mutagenesis in a dam- strain was found to be due to base substitutions, primarily transitions, which had increased 140-fold. Using the trpE997 mutation it was found that the dam mutations also resulted in an increase in frameshift mutagenesis. The mutational spectrum of dam- strains was similar to that found with strains carrying the mutH, mutL, mutS and uvrE mutations thought to result in a defect in the repair of mismatched bases. These results are taken to be consistent with, and to support the hypothesis that, dam- strains are deficient in a post-replicative error-avoidance pathway which allows the directed elimination of mismatch lesions by a mechanism in which parental strands are recognized by their level of DNA methylation.
D000225:Adenine / Q000378:metabolism*; D004269:DNA, Bacterial / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics*; D008745:Methylation; D009154:Mutation; D010641:Phenotype; D010957:Plasmids
D004269:DNA, Bacterial; D000225:Adenine