Physical and functional interactions of human DNA polymerase η with PCNA

Human DNA polymerase eta (hPol eta) functions in the error-free replication of UV-damaged DNA, and mutations in hPol eta cause cancer-prone syndrome, the variant form of xeroderma pigmentosum. However, in spite of its key role in promoting replication through a variety of distorting DNA lesions, the manner by which hPol eta is targeted to the replication machinery stalled at a lesion site remains unknown. Here, we provide evidence for the physical interaction of hPol eta with proliferating cell nuclear antigen (PCNA) and show that mutations in the PCNA binding motif of hPol eta inactivate this interaction. PCNA, together with replication factor C and replication protein A, stimulates the DNA synthetic activity of hPol eta, and steady-state kinetic studies indicate that this stimulation accrues from an increase in the efficiency of nucleotide insertion resulting from a reduction in the apparent K-m for the incoming nucleotide.