The mutagenesis of the major DNA adduct N-(deoxyguanosin-8-yl)-1-aminopyrene (C8-AP-dG) formed by 1-nitropyrene was compared with the analogous C8-dG adducts of 2-aminofluorene (AF) and N-acetyl-2-aminofluorene (AAF) in simian kidney (COS-7) cells. The DNA sequence chosen for this comparison contained 5′-CCATCGCTACC-3′ that has been used for solution NMR investigations. The structural and conformational differences among these lesions are wellestablished (Patel et al., 1998). Accordingly, we found a notable difference in the viability of the progeny, which showed that the AAF adduct was most toxic and the AF adduct was least toxic with the AP adduct exhibiting intermediate toxicity. However, analysis of the progeny showed that translesion synthesis was predominantly error-free. Only low level mutations (<3%) were detected with G→T as the dominant type of mutation by all three DNA adducts. When C8-AP-dG was evaluated in a repetitive 5′-CGCGCG-3′ sequence, higher mutational frequency (~8%) was observed. Again, G→T was the major type of mutations in simian kidney cells, even though in bacteria CpG deletions predominate in this sequence (Hilario et al, 2002). Mutagenesis of C8-AP-dG in a 12-mer containing the local DNA sequence around codon 273 of the p53 tumor suppressor gene, where the adduct was located at the second base of this codon, was also investigated. In this 5′-GTGCGTGTTTGT-3′ site, the mutations were slightly lower but not very different from the progeny derived from the 5′-CGCGCG-3′ sequence. However, the mutational frequency increased by more than 50% when the 5′ C to the adduct was replaced with a 5-methylcytosine (5-MeC). With a 5-MeC, the most notable change in mutation was the enhancement of G→A, which occurred 2.5-times relative to a 5′ C. The C8-AP-dG adduct in codon 273 dodecamer sequence with a 5′ C or 5-MeC was also evaluated in human embryonic kidney (293T) cells. Similar to COS cells, targeted mutations doubled with a 5-MeC 5′ to the adduct. Except for an increase in G→C transversions, the results in 293T were similar to that in COS cells. We conclude that C8-AP-dG mutagenesis depends on the type of cell in which it is replicated, the neighboring DNA sequence, and the methylation status of the 5′ C.