The influence of local DNA sequence and DNA repair background on the mutational specificity of 1-nitroso-8-nitropyrene in Escherichia coli: Inferences for mutagenic mechanisms

We have examined the mutational specificity of 1-nitroso-8-nitropyrene (1,8-NONP), an activated metabolite of the carcinogen 1,8-dinitropyrene, in the lacI gene of Escherichia coli strains which differ with respect to nucleotide excision repair (±ΔuvrB) and MucA/B-mediated error-prone translesion synthesis (±pKM101). Several different classes of mutation were recovered, of which frameshifts, base substitutions, and deletions were clearly induced by 1,8-NONP treatment. The high proportion of point mutations (>92%) which occurred at G · C sites correlates with the percentage of 1,8- NONP-DNA adducts which occur at the C(8) position of guanine. The most prominent frameshift mutations were -(G · C) events, which were induced by 1,8-NONP treatment in all strains, occurred preferentially in runs of guanine residues, and whose frequency increased markedly with the length of the reiterated sequence. Of the base substitution mutations G · C → T · A transversions were induced to the greatest extent by 1,8-NONP. The distribution of the G · C → T · A transversions was not influenced by the nature of flanking bases, nor was there a strand preference for these events. The presence of plasmid pKM101 specifically increased the frequency of G · C → T · A transversions by a factor of 30-60. In contrast, the -(G · C) frameshift mutation frequency was increased only 2-4-fold in strains harboring pKM101 as compared to strains lacking this plasmid. There was, however, a marked influence of pKM101 on the strand specificity of frameshift mutation; a preference was observed for -G events on the transcribed strand. The ability of the bacteria to carry out nucleotide excision repair had a strong effect on the frequency of all classes of mutation but did not significantly influence either the overall distribution of mutational classes or the strand specificity of G · C → T · A transversions and -(G · C) frameshifts. Deletion mutations were induced in the Δuvr, pKM101 strain. The endpoints of the majority of the deletion mutations were G · C rich and contained regions of considerable homology. The specificity of 1,8-NONP- induced mutation suggests that DNA containing 1,8-NONP adducts can be processed through different mutational pathways depending on the DNA sequence context of the adduct and the DNA repair background of the cell.

• View at Pubmed