Repair of DNA containing Fapy·dG and its β-C-nucleoside analogue by formamidopyrimidine DNA glycosylase and MutY

Fapy·dG is produced in DNA as a result of oxidative stress. Under some conditions Fapy·dG is formed in greater yields than 8-oxodG from a common chemical precursor. Recently, Fapy·dG and its C-nucleoside analogue were incorporated in chemically synthesized oligonucleotides at defined sites. Like 8-oxodG, Fapy·dG instructs DNA polymerase to misincorporate dA opposite it in vitro. The interactions of DNA containing Fapy·dG or the nonhydrolyzable analogue with Fpg and MutY are described. Fpg excises Fapy·dG (K_M = 2.0 nM, k_cat = 0.14 min^-1) opposite dC ∼17-fold more efficiently than when mispaired with dA, which is misinserted by DNA polymerase in vitro. Fpg also prefers to bind duplexes containing Fapy·dG·dC or β-C-Fapy·dG·dC compared to those in which the lesion is opposite dA. MutY incises dA when it is opposite Fapy·dG and strongly binds duplexes containing the lesion or β-C-Fapy· dG. Incision from Fapy·dG·dA is faster than from dG·dA mispairs but slower than from DNA containing 8-oxodG opposite dA. These data demonstrate that Fapy·dG closely resembles the interactions of 8-oxodG with two members of the GO repair pathway in vitro. The similar effects of Fapy·dG and 8-oxodG on DNA polymerase and repair enzymes in vitro raise the question as to whether Fapy·dG elicits similar effects in vivo.