The PCNA from Thermococcus fumicolans functionally interacts with DNA polymerase delta

We have cloned the gene encoding proliferating cell nuclear antigen (PCNA) from the hyperthermophilic euryarchaeote Thermococcus fumicolans (Tfu). Tfu PCNA contains 250 amino acids with a calculated M-r of 28,000 and is 26% i dentical to human PCNA. Next, Tfu PCNA was overexpressed in Escherichia col i and it showed an apparent molecular mass of 33.5 kDa. The purified Tfu PC NA was tested first with recombinant Tfu DNA polymerase I (Tfu pol) and sec ond with calf thymus DNA polymerase delta (pol delta). When tested with the homologous Tfu pol on bacteriophage lambda DNA, large amounts of Tfu PCNA were required to obtain two- to threefold stimulation. Surprisingly, howeve r, Tfu PCNA was much more efficient than human PCNA in stimulating calf thy mus pol delta. Our data suggest that PCNA has been functionally conserved n ot only within eukaryotes but also from hyperthermophilic euryarchaeotes to mammals. (C) 2000 Academic Press.