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.

RecQ5 is a member of the RecQ family of DNA helicases. There are 5 RecQ members in humans. Defects in 3 of them, i.e., BLM, WRN, and RTS, cause Bloom, Werner, and Rothmund-Thomson syndromes, respectively. RECQL1 and RECQL5 have not been associated with any human disease, and their precise roles are unknown. Our previous study suggests that the lack of RecQ5, which is the Drosophila homolog of RECQL5, leads to the accumulation of DNA double-stranded breaks (DSBs). It is possible that RecQ5 is involved in DSB repair. However, little is known about this possible function of RecQ5 in DSB repair. Here, we report that Rad51 protein, which plays a critical role in DSB repair, interacted with RecQ5 in vitro and in vivo in Drosophila. The Rad51 protein interacted with the C-terminal region of RecQ5, as shown by the yeast two-hybrid method. Moreover, the C-terminal region of the RecQ5 protein and the central region of Rad51 interacted directly and specifically when examined by the glutathione-S-transferase pull-down method. Consistent with these results, when RecQ5 and Rad51 were co-expressed in Drosophila cells in culture, they became co-localized in nuclei and could be co-immunoprecipitated. Furthermore, RecQ5-deficient flies (recq5) were more sensitive to the chemotherapeutic agent cisplatin compared with wild-type ones. Also, Rad51 mutants (rad51) were more sensitive to cisplatin, with sensitivity similar to that of recq5 rad51 double mutants. These data suggest that RecQ5 and Rad51 in Drosophila functioned for survival after the flies had been treated with cisplatin.Key words RecQ; Rad51; cisplatin; repair; DNA damage; Drosophila RecQ5 is a member of the RecQ family of DNA helicases, in which there are 5 members in humans. Defects in 3 of them, i.e., BLM, WRN, and RTS, cause Bloom, Werner, and Rothmund-Thomson syndromes, respectively, in humans. Genome instability and predisposition to cancer is a common feature of many RecQ helicase-deficient cells. Although RecQL1 and RecQL5 (human homolog of Drosophila RecQ5), the other 2 members of the RecQ family in humans, have not been associated with any human genetic diseases, Recql5-knock out mice show susceptibility to cancer, 1) suggesting that RecQ5 may also play an important role in preventing cancer. However, the precise role of RecQ5 remains unknown.In Drosophila, the frequencies of spontaneous and induced chromosomal aberrations are increased in RecQ5-mutant neuroblasts.2) These data imply that double-stranded break (DSB) damage to DNA accumulates spontaneously in RecQ5 mutants.2) Furthermore, the loss of maternally-derived RecQ5 leads to spontaneous mitotic defects in syncytial embryos. These mitotic defects are derived from anaphase DNA bridges, which link pairs of daughter nuclei. These nuclei concurrently exit from the cycle and are eliminated by Drosophila checkpoint kinase 2 tumor suppressor homolog (DmChk2)-dependent centrosome inactivation.3) DmChk2 responds to DSB DNA lesions. 4) These findings suggest that the lack of RecQ5 results in DSBs, which are recogn...

Members of the RecQ family of DNA helicases are involved in the cellular response to DNA damage and are regulated in the cell-cycle. However, little is known about RecQ5, one of these members. The level of RECQ5/QE, Drosophila melanogaster RecQ5, was increased after the exposure of cultured cells to methyl-methanesulfonate. Transgenic flies that overexpressed RECQ5/QE in their developing eye primordia showed mild roughening of the ommatidial lattice. DNA-damaging agents and the mei-41 mutation enhanced the phenotype caused by RECQ5/QE overexpression. Overexpression of RECQ5/ QE perturbed the progression of the cell-cycle in response to DNA damage in the eye imaginal discs. These results suggest that RECQ5/QE interacts with components of the cell-cycle during its progression in response to DNA damage.