The regulation of Clb5 kinase activity by mating factor

Mating factor was found to affect CIb5 kinase activity in Saccharomyces cer evisiae. Mating factor decreased Clb5 kinase activity in a time- and dose-d ependent manner. The regulation of Clb5 kinase activity requires functional CLNs (G1 cyclins). Strains without functional CLNs still showed sensitivit y to mating factor in the presence of moderately expressing Clb5. This type of mating factor sensitivity is thought to be induced by non-Gl arrest. It is apparent that mating factor treated cells contained inhibitor(s) of CIb 5 kinase activity, suggesting that inhibition of Clb5 kinase activity is ac companied by a specific inhibitor. This notion is supported by mixing exper iment. Nocodazole treatment showed that the effect of mating factor on CIb5 kinase activity occurred at G1 and connected to mitotic exit. Mating facto r regulation of Clb5 kinase activity was found to be dependent on Sic1 prot ein.