Numerous studies have shown that oxidative modifications of guanine (7,8-dihydro-8-oxoguanine, 8-oxoG) can affect cellular functions. 7,8-Dihydro-8-oxoadenine (8-oxoA) is another abundant paradigmatic ambiguous nucleobase but findings reported on the mutagenicity of 8-oxoA in bacterial and eukaryotic cells are incomplete and contradictory. Although several genotoxic studies have demonstrated the mutagenic potential of 8-oxoA in eukaryotic cells, very little biochemical and bioinformatics data about the mechanism of 8-oxoA-induced mutagenesis are available. In this review, we discuss dual coding properties of 8-oxoA, summarize historical and recent genotoxicity and biochemical studies, and address the main protective cellular mechanisms of response to 8-oxoA. We also discuss the available structural data for 8-oxoA bypass by different DNA polymerases as well as the mechanisms of 8-oxoA recognition by DNA repair enzymes.

DNA polymerase θ belongs to the A family of DNA polymerases and plays a key role in DNA repair and damage tolerance, including double-strand break repair and DNA translesion synthesis. Pol θ is often overexpressed in cancer cells and promotes their resistance to chemotherapeutic agents. In this review, we discuss unique biochemical properties and structural features of Pol θ, its multiple roles in protection of genome stability and the potential of Pol θ as a target for cancer treatment.

PrimPol is a human DNA primase and DNA polymerase involved in DNA damage tolerance in both nuclei and mitochondria. PrimPol restarts stalled replication forks by synthesizing DNA primers de novo and also possesses DNA translesion activity (TLS activity). PrimPol efficiently and relatively accurately bypasses several DNA lesions including 8-oxoguanine, thymine glycol and 5-formyluracil. In this work, we showed that PrimPol possesses efficient and accurate TLS activity across 8-oxoadenine, another common DNA lesion caused by oxidative stress. The accuracy of PrimPol on DNA with 8-oxoA was significantly higher compared to DNA containing 8-oxoG. Replacement of Mg²⁺ ions with Mn²⁺ stimulated activity of PrimPol on DNA with 8-oxoA and 8-oxoG as well as undamaged A in a sequence-dependent manner by the lesion skipping (or template scrunching) mechanism. Altogether, our data support the idea that PrimPol possesses efficient TLS activity across a wide range of DNA lesions caused by oxidative stress.

In this work, we analyzed the ability to incorporate 8-oxo-dATP by several human DNA polymerases: replicative Pol ε (exo-) from Family B; base excision repair (BER) enzymes Pol β and Pol λ from Family X; and translesion Pol η, Pol ι, and Pol κ from Family Y. We demonstrated that human DNA polymerases differ in their abilities to discriminate against 8-oxo-dATP. Among the tested DNA polymerases, Pol λ exhibited the worst ability to discriminate against 8-oxo-dATP opposite template T on DNA substrates with a protruding single-stranded 5′-end and a double-stranded DNA with a 1 nt gap. Pol β and DNA polymerases of Family Y showed relatively high accuracy. Pol η demonstrated the most effective discrimination against 8-oxo-dATP on templates T and G. Pol ι exclusively incorporated 8-oxo-dATP opposite template G but not T. Unexpectedly, the catalytic subunit of high-fidelity Pol ε (exo-) incorporated 8-oxo-dATP opposite templates T and G with higher efficiency compared with the error-prone polymerases of Family Y and Pol β. While the structures of human polymerases with incoming 8-oxo-dATP are not available, we speculate on a possible mechanism of 8-oxo-dATP discrimination.

In this work, we analyzed the ability to incorporate 8-oxo-dATP by several human DNA polymerases: replicative Pol ε (exo-), BER enzymes Pol β and Pol λ, and trans-lesion Pol η, Pol ι, and Pol κ. We demonstrated that human DNA polymerases differ in their abilities to discriminate against 8-oxo-dATP. Among tested DNA polymerases, Pol λ demonstrated the worst ability to discriminate against 8-oxo-dATP opposite template T on both singles-stranded DNA and double-stranded DNA substrates with a 1 nt gap. In contrast, Pol β was quite accurate on singe-stranded DNA substrate but incorporated 8-oxo-dATP opposite template T in a 1 nt gap. Unexpectedly, the catalytic subunit of high-fidelity Pol ε (exo-) incorporated 8-oxodATP opposite templates T and G with weak but higher efficiency compare to error-prone polymerases of Family Y. While structures of human polymerases with incoming 8oxo-dATP are not available, we speculate possible mechanism of 8-oxo-dATP discriminations.