Fidelity of Translesional Synthesis past Benzo[a]pyrene Diol Epoxide−2‘-Deoxyguanosine DNA Adducts: Marked Effects of Host Cell, Sequence Context, and Chirality

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Abstract
We have used a site-specific approach to investigate the mutagenic potential of (+)- and (−)-trans-anti-benzo[a]pyrene diol epoxide (BPDE) DNA adducts. Oligodeoxyribonucleotides (5‘TCCTCCTG1G2CCTCTC), modified at the exocyclic amino groups of G1 or G2, were incorporated into a single-stranded shuttle vector and introduced into Escherichia coli or simian kidney (COS) cells. This experimental system permits translesional synthesis to proceed in the absence of DNA repair. The presence of (+)- or (−)-BPDE-N2-dG adducts strongly inhibited translesional synthesis in E. coli; induction of cellular SOS functions reduced this blocking effect. Vectors containing (+)-BPDE adducts at G1 or G2 generated mutation frequencies of 19% and 3%, respectively; these values were not altered significantly by induction of SOS functions. In COS cells, (+)-BPDE-modified vectors generated mutation frequencies of 13% at G1 and 45% at G2. In E. coli, the (−)-BPDE adduct generated mutation frequencies of ≤2% at G1 and G2 and, in COS cells, 13% at G1 and 21% at G2. The predominant mutations in E. coli and COS cells were G→T transversions targeted to the site of the lesion; however, when G2 was modified, a significant number of targeted G→A and G→C mutations were observed in COS cells. We conclude from this study that (+)- and (−)-BPDE-N2-dG adducts pair preferentially to dCMP and dAMP during translesional synthesis in a process that is strongly influenced by the stereochemistry of the adduct, by the bases flanking the lesion, and by host cell factors.