A Role for DNA Polymerase θ in Promoting Replication through Oxidative DNA Lesion, Thymine Glycol, in Human Cells

Background: Little is known of biological functions of DNA polymerase (pol) in human cells. Results: pol promotes replication through the common oxidation product, thymine glycol, in human cells. Conclusion: pol active site can accommodate the considerable distortion imposed by thymine glycol at the extension step. Significance: pol may function in translesion synthesis opposite a variety of DNA lesions. The biological functions of human DNA polymerase (pol) , an A family polymerase, have remained poorly defined. Here we identify a role of pol in translesion synthesis (TLS) in human cells. We show that TLS through the thymine glycol (TG) lesion, the most common oxidation product of thymine, occurs via two alternative pathways, in one of which, polymerases and function together and mediate error-free TLS, whereas in the other, pol functions in an error-prone manner. Human pol is comprised of an N-terminal ATPase/helicase domain, a large central domain, and a C-terminal polymerase domain; however, we find that only the C-terminal polymerase domain is required for TLS opposite TG in human cells. In contrast to TLS mediated by pol and pol, in which pol would elongate the chain from the TG:A base pair formed by pol action, the ability of pol alone to carry out the nucleotide insertion step, as well as the subsequent extension step that presents a considerable impediment due to displacement of the 5 template base, suggests that the pol active site can accommodate highly distorting DNA lesions.