DNA HELICASE ACTIVITY IN WERNERS-SYNDROME GENE-PRODUCT SYNTHESIZED INA BACULOVIRUS SYSTEM

The gene responsible for Werner's syndrome (WRN) contains a region hom ologous to the Escherichia coli RecQ type DNA helicase and was thought to code for a DNA helicase belonging to this helicase family, However , no evidence has been shown before to substantiate this prediction, H ere, we show data that the product of the WRN gene is indeed a DNA hel icase, The gene product, a polypeptide with a relative molecular mass of 170 kDa, expressed in the insect Spodoptera frugiperda (Sf21) cell and purified by affinity column chromatography contained both the ATPa se and DNA unwinding activities characteristic of DNA helicase, Expres sions in Sf21, as well as in HeLa cells, showed that the WRN DNA helic ase is exclusively transported to the nucleoplasm, which is consistent with its function in DNA metabolism, Our studies on strand displaceme nt suggest that WRN helicase can unwind not only a duplex DNA, but als o an RNA-DNA heteroduplex, while the latter reaction seems less effici ent, Enzymological features learned from the purified WRN helicase are discussed with respect to the biological function, which remains to b e clarified.