Studies on the roles of RecQ family proteins in DNA repair and recombination in relation to carcinogenesis and aging

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There exist at least three RecQ homologues in higher eukaryotic cells, DNA helicase Q1, the Bloom's syndrome gene and Werner's syndrome gene product. To clarify the functions of the eukaryotic Rec Q family DNA helicases in DNA repair and recombination and to get an insight into the molecular bases of Bloom's syndrome and Werner's syndrome, we analyzed expression of mRNAs of RecQ family proteins and DNA topoisomerase III which is speculated to function with RecQ helicases, and searched proteins which interact with RecQ family proteins. In addition, we analyzed functional domains of RecQ helicases using gene disruptants of SGS1, which is the yeast RecQ homologue.1. We cloned cDNAs encoding mouse DNA helicase Q1, Bloom's syndrome helicase, DNA topoisomerase IIIalpha and a novel DNA topoisomerase III, IIIbeta (TOP3 beta). We found that messages of these four proteins were highly expressed in the testis. The levels of these mRNAs in the testis increased after birth when the cells in the pachytene phase began to appear and increase.2. We screened for proteins using the yeast two-hybrid system with mouse Wrn as bait and identified three proteins. One is a novel protein, Wip1 (Werner interacting protein 1) and the other two are UBC9 and SUMO-1 (small ubiquitin-related modifier-1), indicating that the function of Werner helicase is regulated by the SUMO- 1 conjugation system.3. We introduced mutations, which were found in the genes of Bloom's syndrome and Werner's syndrome patients, into SGS1 gene and analyzed phenotypes of the yeasts transfected with mutated genes. We found that two different mechanisms are operated in RecQ functions, one requiring DNA helicase activity and one not.