THE MAJOR, N-2-DG ADDUCT OF (-ANTI-B[A]PDE SHOWS A DRAMATICALLY DIFFERENT MUTAGENIC SPECIFICITY (PREDOMINANTLY, G-]A) IN A 5'-CGT-3' SEQUENCE CONTEXT())

Mutations induced by the (+)-anti diol epoxide of benzo[a]pyrene [(+)a nti-B[al]PDE] were described previously in the supF gene of the Escher ichia coli plasmid pUB3 [Rodriguez st al. (1993) Biochemistry, 32, 175 9]. (+)-anti-B[a]PDE induced a complex pattern of mutations, including insertions, deletions, frameshifts, as well as base substitution muta tions, which for G:C base pairs alone included a significant fraction of G:C --> T:A, A:T and C:G mutations. A variety of results suggest th at most of these mutations arise from the major adduct ([+ta]-B[a]P-N- 2-dG), raising the question how can a single adduct induce different k inds of mutations? Our working hypothesis in this regard is that (I) a n adduct can adopt multiple conformations; (2) different conformations cause different mutations; and (3) adduct conformation is controlled by various factors, such as DNA sequence context. To investigate what conformation is associated with what mutation, it is essential to find examples where [+ta]-B[a]P-N-2-dG induces principally one kind of mut ation as a prelude to the study in that same context of the conformati on(s) potentially relevant to mutagenesis. Earlier work indicated that (+)-anti-B[a]PDE gave a preponderance of G --> A mutations in a 5'-C (G) under bar T-3 sequence context, and herein it is shown that these mutations are likely to be attributable to the major adduct, since in this same sequence context [+ta]-B[a]P-N-2-dG studied site specificall y also induces principally G --> A mutations (similar to 82%), Previou sly, [+ta]-B[a]P-N-2-dG was shown to induce principally G --> T mutati ons (similar to 97%) in a 5'-T (G) under bar C-3' sequence context. Th us, by simply altering its surrounding sequence context this adduct ca n give a preponderance elf either G --> A or G --> T mutations. This i s the most dramatic change in base substitution mutagenic specificity for an adduct described to date and illustrates that the qualitative p attern of mutagenesis by a bulky adduct can be remarkably diverse.