Specificity of mutagenesis by 4-aminobiphenyl: mutations at G residues in bacteriophage M13 DNA and G-->C transversions at a unique dG(8-ABP) lesion in single-stranded DNA

Mutagenesis by the human bladder carcinogen 4-aminobiphenyl (ABP) wasstudied in single-stranded DNA from a bacteriophage M13 cloning vector. Incomparison to ABP lesions in double-stranded DNA, lesions in single-stranded DNA were approximately 70-fold more mutagenic and 50-fold moregenotoxic. Sequencing analysis of ABP-induced mutations in the lacZ generevealed exclusively base-pair substitutions, with over 80% of themutations occurring at G sites; the G at position 6310 accounted for 25% ofthe observed mutations. Among the sequence changes at G sites, G- ->Ttransversions predominated, followed by G-->C transversions and G-->A transitions. In order to further elucidate the mutagenic mechanism ofABP, an oligonucleotide containing the major DNA adduct, N-(deoxyguanosin-8-yl)-4-aminobiphenyl (dG(8-ABP)), was situated within thePstI site of a single-stranded M13 genome. After in vivo replication of theadduct containing ABP-modified and control (unadducted) genomes, themutational frequency and mutational specificity of the dG(8-ABP) lesionwere determined. The targeted mutational efficiency was approximately0.01%, and the primary mutation observed was the G-->C transversion.Thus dG(8-ABP), albeit weakly mutagenic at the PstI site, can contribute tothe mutational spectrum of ABP lesions.