Yeast DNA polymerase η makes functional contacts with the DNA minor groove only at the incoming nucleoside triphosphate

DNA polymerase η (Polη) functions in the proficient bypass of a variety of DNA lesions. Relative to the replicative polymerases, Polη has a greater tolerance for distorted DNA geometries and possesses a low fidelity. X-ray crystal structures and studies with nucleotide analogs have implicated interactions with the DNA minor groove as being crucial for the high fidelity of replicative DNA polymerases. To determine whether Polη also makes such functionally important contacts with the DNA minor groove, here we examine the effects on Polη-catalyzed nucleotide incorporation when 3-deazaguanine, a base analog that lacks the ability to form minor-groove hydrogen bonds with the protein, is substituted for guanine at various positions in the DNA. From these studies, we conclude that Polη makes only a single functional contact with the DNA minor groove at the position of the incoming nucleotide; in this regard, Polη differs from high-fidelity DNA polymerases that are unable to replicate through DNA lesions. These results help explain the proficient ability of Polη for bypassing distorting DNA lesions.