The PCL2 (ORFD)-PHO85 Cyclin-Dependent Kinase Complex: a Cell Cycle Regulator in Yeast

Abstract

Cyclin-dependent kinase (cdk) complexes are essential activators of cell cycle progression in all eukaryotes. In contrast to mammalian cells, in which multiple cdk's contribute to cell cycle regulation, the yeast cell cycle is largely controlled by the activity of a single cdk, CDC28. Analysis of the putative G1 cyclin PCL2 (ORFD) identified a second cyclin-cdk complex that contributes to cell cycle progression in yeast. PCL2 interacted with the cdk PHO85 in vivo and in vitro and formed a kinase complex that had G1-periodic activity. Under genetic conditions in which the Start transition was compromised, PHO85 and its associated cyclin subunits were essential for cell cycle commitment. Because PHO85 and another cyclin-like molecule, PHO80, also take part in inorganic phosphate metabolism, this cdk enzyme may integrate responses to nutritional conditions with the cell cycle.

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

“…4, lane 4). Together, these results show that Pcl9 interacts with Pho85 and behaves in a manner similar to other Pcls tested in this assay (Measday et al, 1994). These results are consistent with our previous work using a GST pull-down assay in which GST-Pho85 was shown to interact with in vitro translated Pcl9 .…”

“…4, lane 3). A similar experiment was carried out using an antibody to Pho85 that immunoprecipitates Pho85 but interferes with cyclin binding (Measday et al, 1994). As expected, the antibody immunoprecipitated Pho85 (Fig.…”

“…Pho85 is also involved in regulation of the G 1 phase of the cell cycle when complexed with the cyclins Pcl1 and Pcl2 (Espinoza et al, 1994;Measday et al, 1994). The decision to enter the cell cycle occurs in late G 1 phase and is primarily controlled by the cyclin-dependent kinase CDC28 and its associated G1 cyclins CLN1, 2 and 3 (reviewed in Cross, 1995b;Nasmyth, 1996).…”

“…The decision to enter the cell cycle occurs in late G 1 phase and is primarily controlled by the cyclin-dependent kinase CDC28 and its associated G1 cyclins CLN1, 2 and 3 (reviewed in Cross, 1995b;Nasmyth, 1996). Although cells lacking PCL1 and PCL2 are viable, Pcl1,2-Pho85 complexes are required for cell cycle progression in the absence of CLN1 and CLN2, suggesting a role for these complexes at START (Espinoza et al, 1994;Measday et al, 1994;. A role for PCL1,2 in G 1 phase is supported by other observations: (i) expression of PCL1 and PCL2, like that of CLN1 and CLN2, is controlled by the G 1 -specific regulator SBF, with peak expression at START; (ii) Pcl2-Pho85 kinase activity peaks in G 1 phase (Measday et al, 1994); and (iii) overexpression of PCL1 and PCL2 rescues the lysis defect in slt2 mutants (Madden et al, 1997).…”

“…Although cells lacking PCL1 and PCL2 are viable, Pcl1,2-Pho85 complexes are required for cell cycle progression in the absence of CLN1 and CLN2, suggesting a role for these complexes at START (Espinoza et al, 1994;Measday et al, 1994;. A role for PCL1,2 in G 1 phase is supported by other observations: (i) expression of PCL1 and PCL2, like that of CLN1 and CLN2, is controlled by the G 1 -specific regulator SBF, with peak expression at START; (ii) Pcl2-Pho85 kinase activity peaks in G 1 phase (Measday et al, 1994); and (iii) overexpression of PCL1 and PCL2 rescues the lysis defect in slt2 mutants (Madden et al, 1997). Slt2 encodes a MAP kinase that is involved in maintaining cell integrity during the polarized cell growth inherent in early cell cycle events, such as bud emergence and mating (reviewed in Levin and Errede, 1995).…”