👤 I Herskowitz

The events of the eukaryotic cell cycle are governed by cyclin-dependent kinases (cdk's), whose activation requires association with cyclin regulatory subunits expressed at specific cell cycle stages. In the budding yeast Saccharomyces cerevisiae, the cell cycle is thought to be controlled by a single cdk, CDC28. Passage through the G1 phase of the cell cycle is regulated by complexes of CDC28 and G1 cyclins (CLN1, CLN2, and CLN3). A putative G1 cyclin, HCS26, has recently been identified. In a/alpha diploid cells lacking CLN1 and CLN2, HCS26 is required for passage through G1. HCS26 does not associate with CDC28, but instead associates with PHO85, a closely related protein kinase. Thus, budding yeast, like higher eukaryotes, use multiple cdk's in the regulation of cell cycle progression. Show less

alpha factor is a negative growth factor and differentiation factor that induces G1 arrest and increases transcription of mating genes in S. cerevisiae a cells. We have identified a gene, FAR1 (for "factor arrest"), which is necessary for cell cycle arrest but not for other responses to alpha factor: far1- mutants are insensitive to arrest despite having an intact signal transduction pathway. FAR1 is a nonessential gene whose expression is induced 4- to 5-fold in a cells by alpha factor. The sequence of FAR1 indicates no significant similarities to known proteins. A null mutation in the CLN2 gene, which codes for a G1 cyclin, reverses the effect of a far1 null mutation: far1- cln2- strains arrest in response to alpha factor. We thus propose that FAR1 contributes to cell cycle arrest by inhibiting CLN2. The behavior of far1- cln2- strains indicates that products other than FAR1 are responsible for inhibiting the other G1 cyclins, CLN1 and CLN3. Show less