Stimulation of DNA synthesis activity of human DNA polymerase κ by PCNA

Humans have three DNA polymerases, Polη, Polκ, and Polι, which are able to promote replication through DNA lesions. However, the mechanism by which these DNA polymerases are targeted to the replication machinery stalled at a lesion site has remained unknown. Here, we provide evidence for the physical interaction of human Polκ (hPolκ) with proliferating cell nuclear antigen (PCNA) and show that PCNA, replication factor C (RFC), and replication protein A (RPA) act cooperatively to stimulate the DNA synthesis activity of hPolκ. The processivity of hPolκ, however, is not significantly increased in the presence of these protein factors. The efficiency (V_max/K_m) of correct nucleotide incorporation by hPolκ is enhanced ∼50- to 200-fold in the presence of PCNA, RFC, and RPA, and this increase in efficiency is achieved by a reduction in the apparent K_m for the nucleotide. Although in the presence of these protein factors, the efficiency of the insertion of an A nucleotide opposite an abasic site is increased ∼ 40-fold, this reaction still remains quite inefficient; thus, it is unlikely that hPolκ would bypass an abasic site by inserting a nucleotide opposite the site.