Targeting of human DNA polymerase ι to the replication machinery via interaction with PCNA

Human DNA polymerase i (hPoli) promotes translesion synthesis by inserting nucleotides opposite highly distorting or noninstructional DNA lesions. Here, we provide evidence for the physical interaction of hPoli with proliferating cell nuclear antigen (PCNA), and show that PCNA, together with replication factor C (RFC) and replication protein A (RPA), stimulates the DNA synthetic activity of hPoli. In the presence of these protein factors, on undamaged DNA, the efficiency (V-max/K-m) of correct nucleotide incorporation by hPoli is increased approximate to 80-150-fold, and this increase in efficiency results from a reduction in the apparent K-m for the nucleotide. PCNA, RFC, and RPA also stimulate nucleotide incorporation opposite the 3'-T of the (6-4) thymine-thymine (T-T) photoproduct and opposite an abasic site. The interaction of hPoli with PCNA implies that the targeting of this polymerase to the replication machinery stalled at a lesion site is achieved via this association.