Role of human DNA polymerase kappa as an extender in translesion synthesis

Human DNA polymerase (Pol)kappa is a member of the Y family of DNA polymerases. Unlike Poleta, another member of this family, which carries out efficient translesion synthesis through various DNA lesions, the role of Polkappa in lesion bypass has remained unclear. Recent studies, however, have indicated that Polkappa is a proficient extender of mispaired primer termini on undamaged DNAs and also on cis-syn thymine-thymine (T-T) dimer-containing DNA. Here we determine whether Polkappa can promote the efficient bypass of DNA lesions by extending from the nucleotides inserted opposite the lesion site by another DNA polymerase. From steady-state kinetic analyses, we find that Polkappa is highly inefficient at incorporating nucleotides opposite an O(6)-methyl guanine (m6G) lesion, but it efficiently extends from the T or C nucleotide incorporated opposite this lesion by Poldelta. Opposite an 8-oxoguanine (8-oxoG) lesion, Polkappa efficiently inserts an A and then proficiently extends from it. Importantly, for both these DNA lesions, however, the most efficient bypass occurs when Poldelta is combined with Polkappa; in this reaction, Polkappa performs the extension step after the incorporation of nucleotides opposite these lesion sites by Poldelta. These studies reveal a role for Polkappa in the extension phase of lesion bypass.