A role for the Pcl9‐Pho85 cyclin–cdk complex at the M/G₁ boundary in Saccharomyces cerevisiae

Abstract

SummaryPHO85 is a cyclin-dependent kinase (CDK) with roles in phosphate and glycogen metabolism and cell cycle progression. As a CDK, Pho85 is activated by association with Pho85 cyclins (Pcls), of which 10 are known. PCL1, PCL2 and PCL9 are the only members of the Pho85 cyclin family that are expressed in a cell cycleregulated pattern. We found that PCL9 is expressed in late M/early G 1 phase of the cell cycle and is activated by the transcription factor, Swi5. This pattern of regulation is different from PCL1 and PCL2, which are expressed later in G 1 phase and are regulated primarily by the transcription factor SBF. Co-immunoprecipitation experiments using in vitro translated proteins showed that Pcl9 and Pho85 form a complex. Furthermore, immunoprecipitated Pcl9 complexes from yeast lysates were capable of phosphor ylating the exogenous substrate Pho4. The Pcl9-associated kinase activity was dependent on PHO85, showing that Pcl9 and Pho85 form a functionally active kinase complex in vivo. Deletion of PCL9 in diploid cells caused random, rather than bipolar, budding in 18% of cells. In contrast, deletion of PCL2, the closest relative of PCL9, had no effect on the budding pattern. Deleting more members of the PCL1,2 subfamily (which includes PCL9 ) increased the percentage of random budding in the cell population. When all members of the PCL1,2 subfamily were deleted, 73% of cells budded randomly, a value similar to that obtained when the CDK partner PHO85 was deleted. Our results show that PCL9 and PHO85 form a functional kinase complex and suggest a role for Pho85 CDKs at the M/G 1 boundary.

Cell Polarization and Cytokinesis in Budding Yeast

“…A similar phenomenon is also observed in other bipolar mutants including spa2 and bud6/aip3 (Zahner et al 1996). Bipolar budding is also disrupted by mutations in many other genes, which may affect bipolar budding indirectly (Snyder 1989;Sivadon et al 1995;Valtz and Herskowitz 1996;Zahner et al 1996;Finger and Novick 1997;Vaduva et al 1997;Yang et al 1997;Sheu et al 1998;Tennyson et al 1998;Bi et al 2000;Ni and Snyder 2001;Tcheperegine et al 2005).…”

Dissection of a Complex Phenotype by Functional Genomics Reveals Roles for the Yeast Cyclin-Dependent Protein Kinase Pho85 in Stress Adaptation and Cell Integrity

“…Also, expression of PCL1, PCL2, and highly related cyclin gene PCL9 is entirely restricted to G 1 phase of the cell cycle, consistent with roles for these kinases in G 1 phase progression (1,40,61). Several observations suggest that the essential function of G 1 -specific Pcl-Pho85 complexes relates to cell polarity and morphogenesis.…”

Life in the midst of scarcity: adaptations to nutrient availability in Saccharomyces cerevisiae

“…Deletion of PHO85 results in slow growth with a G 1 -delay on rich medium and a severe growth defect on poor carbon and nitrogen sources (Lee et al 2000). More specifically, mutant pho85D cells display a background-dependent hyperaccumulation of glycogen (Timblin et al 1996;Lee et al 2000), morphology and polarity defects (Measday et al 1997;Tennyson et al 1998), constitutive expression of phosphate-responsive or so-called PHO genes, CWI defects and hypersensitivity to stress conditions (Huang et al 2002), sporulation defects (Gilliquet and Berben 1993), aberrant expression profiles during the diauxic shift (Nishizawa et al 2004) and a hyperinduction of nutrient starvation-induced autophagy (Wang et al 2001). Consistent with its multiple functions, Pho85 can interact with ten different cyclins that can be divided into two different subfamilies according to their sequence similarities (Measday et al 1997).…”