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Disruption of mitochondrial DNA polymerase γ replication by the aldehyde adduct of DNA, M1dG

M1dG is a mutagenic adduct generated in human nuclear and mitochondrial DNA (mtDNA) by reaction of the cellular peroxidation products, malondialdehyde and base propenal, with guanine. Since M1dG is known to interfere with DNA synthesis by replicative and Y‐family DNA polymerases, we have utilized recombinant exonuclease‐deficient human DNA polymerase γ (exo− pol γ) with or without its accessory subunit p55 to investigate the effects of the adduct on mtDNA synthesis. Using primer‐templates that required exo−pol γ to extend the primer by insertion opposite the adduct position, we found that M1dG decreased exo− pol γ primer extension by 50% and prevented synthesis of a fully‐extended 35‐mer primer. A dAMP was inserted preferentially opposite M1dG, but extension of the primer past the adduct was supported only by dCMP incorporation. The insertion efficiency for exo− pol γ with either dCTP or dATP as substrates was substantially reduced by M1dG, and p55 had no effect on exo−pol γ nucleotide selection or insertion kinetics at the adduct. Since human mitochondria have no known mechanism for repair of M1dG, which is a target of nucleotide excision repair in the nucleus, our data indicate that the endogenous adduct poses a significant threat to mtDNA stability by disrupting DNA pol γ replication. (Supported by National Institutes of Health Grants GM087681 to S.D.C. and CA087819 to L.J.M, and NIH intramural funding to W.C.C.)