Separable roles of saccharomtces cerevsiae ste5 in gl cell cycle arrest and mating

M it ogen activated proteinf M APK t palhwav is an important net work for cell proliferation and differentiation. In budding yeast .V. nnntiat at lea M .six physiologically distinct MAPK cascades were identified. Among these, p heroin one mediated signaling pat h way is most well characterized and \} involved in both Gl cell tyck1 arn-4t and mating of t lie S. ctrrriiiat. Steî. to gether with Ste20, Stell and Ste7, is essential for the activation of the MAPK homolog. FuslJ. in pherornone induced signal t ransduct ion cascade in .V. /( ni'iniüf Steö physically links the protein kinases by forming the complex for t he regulation of the pheromone signaling pathway and may endow specificity fui the pathway. To understand the roles of Sten better we isolated Gl cell cycle .irrest xte-î mutants by chemical mut agenesis. Two of the tt ,r> mut ants( 1)₂4 XV and A-770} mate normally although it completely lost Gl cell cvcle arrest function. Therefore these t< > mutation,-, affects only t lie (II arrest function Furthermore, most of our cell cycle arres detective ,s/('"> mutants show dom inant negative phenotype when transforiüed into a wild typp $'TI'.\l>+ strain. However, all of the Gl arrest detective .sf" .> mutant-4 show recessive pheno l\pe for mating. These resiilth Miggest.s roles of Sleri in cell cycle arrest and mating arc separable. Biochemical .inalvsis of Gl arrest defective mutant-4 show o factor dependent StefvFus.i interaction may important for (l arrest phenotype and activation of His'l kinasc.