The influence of excision repair on the distribution of N-propyl-N'-nitro-N-nitrosoguanidine-induced mutation in Escherichia coli.

To determine the influence of excision repair on the distribution of N-propyl-N'-nitro-N-nitrosoguanidine (PNNG)-induced mutation, we have analysed the DNA sequence changes of mutation induced at the lacI gene of Escherichia coli in a UvrB- strain. The mutagenic specificity was similar to that found in the wild-type strain. Base substitutions predominate; G:C----A:T transitions accounted for almost 75% of the mutational events, while G:C----T:A transversions constituted approximately 20% of the mutations. In both strains the distribution of G:C----A:T transitions was nonrandom, but the site specificity of the G:C----A:T transitions appear dissimilar, with the hot and cold sites occurring at different positions. A single - 1 frameshift was recovered in each strain but deletion events were absent in the excision-repair-deficient strain. The complexity of the sequence-specificity of PNNG might reflect the differential repair of n-propyl and iso-propyl adducts.