Influence of flanking sequence context on the mutagenicity of acetylaminofluorene-derived DNA adducts in mammalian cells

Site-specifically modified oligodeoxynucleotides were used to explore the influence of neighboring base sequence context on the mutagenic potential of N-(deoxyguanosin-8-yl)-2-acetylaminofluorene (dG-AAF) and N-(deoxyguanosin-8-yl)-2-aminofluorene (dG-AF) in mammalian cells. Oligodeoxynucleotides (^5′TCCTCCTNXNCTCTC, where X is dG-AAF, dG-AF, or dG and N is C, A, G, or T) with different bases flanking the lesion were incorporated into a single-strand shuttle plasmid vector and used to establish the mutational frequency and specificity of dG-AAF and dG-AF adducts in simian kidney (COS-7) cells. Vectors containing dG-AAF promote preferential incorporation of dCMP at the site of the lesion; misincorporation of dAMP and dTMP also was observed. Mutational frequencies range from 11 to 23%. High mutational frequencies (18-23%) were observed when G or T was positioned 5′ to dG-AAF and a lower frequency (11%) when C was 5′ to the lesion, dCMP was predominantly incorporated opposite the dG-AF adduct when C, A, or T was 5′ to the lesion; dAMP and dTMP were misincorporated at a frequency of 2-4%. With G 5′ to the lesion, the overall mutational frequency for dG-AF ranged between 11 and 70%; the highest value occurred when C was the 3′ flanking base, and the predominant mutation event was G → T transversion (59%). We conclude from these experiments that dG-AAF and dG-AF promote G → T transversions and G → A transitions in mammalian cells. The mutational frequency and specificity of dG-AF vary significantly, depending on the nature of the bases flanking the lesion.