A YEAST GENE-PRODUCT, G4P2, WITH A SPECIFIC AFFINITY FOR QUADRUPLEX NUCLEIC-ACIDS

G4 nucleic acids are quadruplex structures involving guanine-rich sequ ences that form in vitro under moderate conditions. Experimental evide nce exists supporting biological functions for these elements; however , direct demonstration of G4 nucleic acids in vivo has not yet been ac hieved, Here we purify and characterize a yeast protein, G4p2, which h as a specific affinity for G4 nucleic acids, G4p2 binds equivalently t o RNA and DNA in G4 form. The K-eq for G4p2 binding to a G4 DNA oligom er is 2.2 x 10(8) M(-1) under near physiological conditions, We have c loned and sequenced the gene encoding G4p2 and have shown it to be ide ntical to MPT4 and STO1, MPT4 was isolated in a screen for multicopy s uppressors of staurosporine sensitivity in POP2 cells, Pop2 is a compl ex regulatory factor that participates, in part, in the repression of certain genes in the absence of glucose (Sakai, A., Chibazakura, T., S himizu, Y., and Hishinuma, F. (1992) Nucleic Acids Res. 20, 6227-6233) , STO1 was isolated as a multicopy suppressor of TOM1, an uncharacteri zed mutation that leads to temperature sensitive cell cycle arrest at the G2/M boundary, Suppression of these mutations by G4p2 indicate thi s G4 nucleic acid binding protein may function in signal transduction pathways regulated by protein kinases, which control carbon source uti lization, and in cell cycle progression.