Abstract
The Drosophila melanogaster RECQ5/QE gene encodes a member of the DNA helicase family comprising the Escherichia coli RecQ protein and products of the human Bloom's, Werner's, and Rothmund-Thomson syndrome genes. The full-length product of RECQ5/QE was expressed in the baculovirus system and was purified. Gel filtration experiments indicated that RECQ5/QE was present in an oligomeric state. The RECQ5/QE protein hydrolyzed ATP and even more actively GTP in the presence of single-stranded DNA. ATP drove the DNA helicase activity of RECQ5/QE, whereas GTP had little effect. GTP exhibited a stimulatory effect on DNA unwinding when it was used together with ATP. This effect was more apparent with non-hydrolyzable GTP analogs, such as GTPgammaS and GMPPNP. These results indicate that GTP binding to RECQ5/QE triggers its DNA helicase activity. GTP binding increased the rate of strand separation without affecting the S(0.5) (K(m)) values for the substrates during the DNA helicase reaction. The data collectively suggest that the RECQ5/QE protein is activated upon GTP binding through the ATP-binding site.