Replication factor C-mediated stimulation of flap endonuclease 1

Abstract

Flap endonuclease 1 (FEN1) is a structure-specific endonuclease that removes flap structure arising in several DNA metabolisms such as DNA replication, repair and recombination. In this study, we report that human replication-factor C (RFC) complex markedly stimulated all types of nuclease activities of human FEN1 (FEN1) in an ATP-independent manner. The amount of RFC was much less (<200 fold) than that of proliferating cell nuclear antigen (PCNA) in order to stimulate FEN1 to a comparable extent. Various kinetic parameters indicate that the mechanism by which RFC stimulates FEN1 is distinct from that by PCNA. Each subunit of RFC retained stimulation activity of FEN1, fully or partially, even when it was heat denatured. With systematic deletion analyses of RFC4 subunit, we defined three regions that were able to stimulate FEN1. The strongest stimulation one comprised amino acids 170 to 194 in RFC4 that contained RFC box VII. We also found that the four residues Tyr182, Glu188, Pro189, and Ser192 were critical for FEN1 stimulation. Therefore, the presence of a number of stimulatory motifs in one molecule of RFC and its ability to stimulate FEN1 greatly at low levels render RFC a critical partner for catalytic function of FEN1 required for processing of Okazaki fragments in eukaryotes.