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Error‐prone replication bypass of the imidazole ring‐opened formamidopyrimidine deoxyguanosine adduct

Addition of hydroxyl radicals to the C8 position of 2′‐deoxyguanosine generates an 8‐hydroxyguanyl radical that can be converted into either 8‐oxo‐7,8‐dihydro‐2′‐deoxyguanosine or N‐(2‐deoxy‐d‐pentofuranosyl)‐N‐(2,6‐diamino‐4‐hydroxy‐5‐formamidopyrimidine) (Fapy‐dG). The Fapy‐dG adduct can adopt different conformations and in particular, can exist in an unnatural α anomeric configuration in addition to canonical β configuration. Previous studies reported that in 5′‐TGN‐3′ sequences, Fapy‐dG predominantly induced G → T transversions in both mammalian cells and Escherichia coli, suggesting that mutations could be formed either via insertion of a dA opposite the 5′ dT due to primer/template misalignment or as result of direct miscoding. To address this question, single‐stranded vectors containing a site‐specific Fapy‐dG adduct were generated to vary the identity of the 5′ nucleotide. Following vector replication in primate cells (COS7), complex mutation spectra were observed that included ∼3–5% G → T transversions and ∼14–21% G → A transitions. There was no correlation apparent between the identity of the 5′ nucleotide and spectra of mutations. When conditions for vector preparation were modified to favor the β anomer, frequencies of both G → T and G → A substitutions were significantly reduced. Mutation frequencies in wild‐type E. coli and a mutant deficient in damage‐inducible DNA polymerases were significantly lower than detected in COS7 and spectra were dominated by deletions. Thus, mutagenic bypass of Fapy‐dG can proceed via mechanisms that are different from the previously proposed primer/template misalignment or direct misinsertions of dA or dT opposite to the β anomer of Fapy‐dG. Environ. Mol. Mutagen. 58:182–189, 2017. © 2017 Wiley Periodicals, Inc.