Werner syndrome protein interacts with human flap endonuclease 1 and stimulates its cleavage activity

Werner syndrome (WS) is a human premature aging disorder characterized by chromosomal instability. The cellular defects of WS presumably reflect compromised or aberrant function of a DNA metabolic pathway that under normal circumstances confers stability to the genome. We report a novel interaction of the WRN gene product with the human 5′ flap endonuclease/5′–3′ exonuclease (FEN‐1), a DNA structure‐specific nuclease implicated in DNA replication, recombination and repair. WS protein (WRN) dramatically stimulates the rate of FEN‐1 cleavage of a 5′ flap DNA substrate. The WRN–FEN‐1 functional interaction is independent of WRN catalytic function and mediated by a 144 amino acid domain of WRN that shares homology with RecQ DNA helicases. A physical interaction between WRN and FEN‐1 is demonstrated by their co‐immunoprecipitation from HeLa cell lysate and affinity pull‐down experiments using a recombinant C‐terminal fragment of WRN. The underlying defect of WS is discussed in light of the evidence for the interaction between WRN and FEN‐1.