Mutagenic specificity of reductively activated 1-nitropyrene in Escherichia coli

1-Nitropyrene (1-NP), the predominant nitropolycyclic hydrocarbon found in diesel exhaust, is a mutagen and tumorigen. Nitroreduction is a major pathway by which 1-NP is metabolized. In order to study the distribution of DNA adducts and the mutational specificity of reductively activated 1-NP, single stranded M13mp18 DNA was treated with N-hydroxyl-1-aminopyrene generated in situ to give > 95% of one major adduct, N-(deoxyguanosin-8-yl)-1-aminopyrene. A primer was annealed to DNA containing different levels of adducts, and polymerase extension on these templates was studied. Replication inhibition, primarily at or 3' to guanine bases, was observed. Transfection of these M13 DNA in Escherichia coli indicated a dose-dependent reduction in viability with concomitant enhancement in mutagenesis in the lacZ gene fragment. Approximately two adducts per genome constituted one lethal hit (approximately 37% viability). Both survival and mutagenesis were increased when SOS functions of the host cell were induced. N-(Deoxyguanosin-8-yl)-1-aminopyrene mutagenesis appeared to be SOS-dependent. With SOS induction, one-base deletions and insertions were the major event (45%), although base substitutions also occurred at high frequency (44%). A major proportion of the point mutations, and particularly one-base deletions and insertions, were detected in 5'-CG, 5'-GC, or 5'-GG sequences. Analysis of the mutation data suggested that N-(deoxyguanosin-8-yl)-1-aminopyrene-induced mutations occurred predominantly at the adduct site, but mutations at the base located next to it have been detected at a significant frequency as well. A large fraction of point mutations occurred in a hairpin loop region.(ABSTRACT TRUNCATED AT 250 WORDS)