Mutation in Escherichia coli and mammalian cells induced by closely spaced 1-methylpyrene-deoxyadenosine adducts in opposite DNA strands.
Twenty-eight base complementary oligonucleotides were synthesized with deoxyadenosine residues modified at the N6 position with 1-methylpyrene (MP) specifically positioned 3 bp apart in opposite DNA strands. Doubly modified constructs as well as non-modified and singly modified constructs were ligated into M13mp19 and an SV40-based shuttle vector pSVL-lac for transfection into Escherichia coli and large T-antigen-expressing monkey kidney epithelial cells respectively. Repair of MP adducts was analyzed by direct nucleotide sequencing after selection of clones containing the 28mer construct. In E. coli, double MP adducts induced base substitutions at positions mainly adjacent to modified adenines, while single MP adducts were not mutagenic. Single base insertions were also induced proximal to modified adenines. The frequency of mutation induced by double MP adducts in E. coli was approximately 4% (eight mutations out of 196 analyzed). In monkey kidney cells, double MP adducts induced one and three base deletions and single base insertions. Base substitution was observed in constructs containing non-modified and singly modified adenine residues, indicative of a significant spontaneous mutation rate. The frequency of mutation induced by double MP adducts in monkey kidney cells was approximately 9% (six mutations out of 66 clones analyzed). Modification of adenine residues by MP caused termination of DNA replication by E. coli DNA polymerase I (Klenow fragment) in vitro at the position opposite the MP adduct and at the preceding base. The repair of closely spaced polycyclic aromatic hydrocarbon adducts in opposite DNA strands is discussed as it relates to mutagenesis and carcinogenesis in mammalian cells.