Mutagenic potential of guanine N² adducts of butadiene mono- and diolepoxide

To explore the role of guanine N² adducts of stereoisomeric butadiene metabolites in butadiene-induced mutagenesis, 11-mer deoxyoligonucleotides were prepared containing adducts of (R)- and (S)-monoepoxide and (R,R)- and (S,S)-diolepoxide. These adducted oligonucleotides were utilized in both in vivo and in vitro experiments designed to examine the mutagenic potency of each and their replication by Escherichia coli polymerases. Each of the four adducted deoxyoligonucleotides was ligated into a single-stranded M13mp7L2 vector and transfected into E. coli. The resulting plaques were screened for misincorporation at position 2 of the N-ras 12 codon. Although the mutagenic frequencies were low, different relative mutagenicities of the various stereoisomers were discernible. In addition, the biological effects of each adduct on the three major E. coli polymerases were determined via primer extension assays. The adducted 11-mers were ligated into a 60-mer linear DNA molecule to provide a sufficiently long template for primer elongation. All four guanine adducts were determined to be blocking to each of the three polymerases via primer extension assays.