Functional and physical interaction between WRN helicase and human replication protein A

The human premature aging disorder Werner syndrome (WS) is associated with a large number of symptoms displayed in normal aging. The WRN gene product, a DNA helicase, has been previously shown to unwind short DNA duplexes (le ss than or equal to 53 base pairs) in a reaction stimulated by single-stran ded DNA-binding proteins. We have studied the helicase activity of purified WRN protein on a variety of DNA duplex substrates to characterize the unwi nding properties of the enzyme in greater detail. WRN helicase can catalyze unwinding of long duplex DNA substrates up to 849 base pairs in a reaction dependent on human replication protein A (hRPA). Escherichia coil SSB and bacteriophage T4 gene 32 protein (gp32) completely failed to stimulate WRN helicase to unwind long DNA duplexes indicating a specific functional inter action between WRN and hRPA. So far, there have been no reports of any phys ical interactions between WRN helicase and other proteins. In support of th e functional interaction, we demonstrate a direct interaction between WRN a nd hRPA by coimmunoprecipitation of purified proteins. The physical and fun ctional interaction between WRN and hRPA suggests that the two proteins may function together in vivo in a pathway of DNA metabolism such as replicati on, recombination, or repair.