Cyclin-dependent protein kinase (CDK) catalytic subunit that regulates multiple cell cycle and metabolic processes in response to nutrient availability. Associates with different cyclins, that control kinase activity, substrate specificity and subcellular location of the kinase. Regulates metabolic processes when associated with PHO80 cyclin family members (PH080, PCL6, PCL7, PCL8 and PCL10), and cell cycle and morphogenesis processes when associated with PCL1,2 cyclin family members (PCL1, PCL2, CLG1, PCL5 and PCL9) (PubMed:10490639, PubMed:10692159, PubMed:11602261, PubMed:12006994, PubMed:12098764, PubMed:12101234, PubMed:12407105, PubMed:12857883, PubMed:15057567, PubMed:15082539, PubMed:15598647, PubMed:15721288, PubMed:16308562, PubMed:16455487, PubMed:3067079, PubMed:7973730, PubMed:8108735, PubMed:8539622, PubMed:9584169, PubMed:9593297, PubMed:9725902, PubMed:9843683, PubMed:12455686). When associated with PHO80, negatively regulates the expression of phosphate-starvation-responsive genes under phosphate-rich conditions (PubMed:8108735, PubMed:3067079). The PHO80-PHO85 cyclin-CDK holoenzyme phosphorylates and inactivates the transcription factor PHO4 by promoting its export to the cytoplasm (PubMed:8108735). PHO80-PHO85 phosphorylates and inactivates protein kinase RIM15 by retaining it in the cytoplasm, antagonizing RIM15-induced entry into stationary phase (PubMed:16308562). PHO80-PHO85 also phosphorylates and inactivates the calcineurin-responsive transcription factor CRZ1, linking cyclin-CDK activity to calcium signaling (PubMed:16455487). PHO80-PHO85 phosphorylates MMR1 (PubMed:12006994). Together with the cyclins PCL6/PCL7 and PCL8/PCL10, negatively controls glycogen accumulation (PubMed:10490639, PubMed:11602261, PubMed:15721288, PubMed:8539622, PubMed:9584169, PubMed:12407105). When associated with cyclins PCL6 and PCL7, controls glycogen phosphorylase and glycogen synthase activities (PubMed:11602261, PubMed:15721288, PubMed:12407105). PCL6-PHO85 and PCL7-PHO85 phosphorylate and inactivate the phosphatase PP1-2 inhibitor GLC8, causing activation of PP1-2, which then dephosphorylates and activates glycogen phosphorylase (PubMed:12407105). PCL7-PHO85 phosphorylate ALY2 (PubMed:12098764). PCL10-PHO85 phosphorylates and negatively regulates glycogen synthase GSY2 (PubMed:9584169). Association with PCL1 and PCL2 is required for cell cycle progression at start in the absence of the CDC28-dependent G1 cyclins CLN1 and CLN2 (PubMed:7973730, PubMed:7973731). PCL1-PHO85 is involved in phosphorylation of the CDK inhibitor (CKI) SIC1, which is required for its ubiquitination and degradation, releasing repression of b-type cyclins and promoting exit from mitosis (PubMed:9725902). When associated with cyclins PCL1 and PCL2, positively controls degradation of sphingoid long chain base kinase LCB4 via phosphorylation of LCB4, which is required for its ubiquitination and degradation (PubMed:15598647). PCL1-PHO85 also phosphorylates HMS1, NCP1 and NPA3, which may all have a role in mitotic exit (PubMed:15082539). PCL2-PHO85 also phosphorylates RVS167, linking cyclin-CDK activity with organization of the actin cytoskeleton (PubMed:9843683, PubMed:12857883). When associated with PCL5, positively controls degradation of transcription factor GCN4 via phosphorylation of GCN4, which is required for its degradation by the E3 ubiquitin ligase complex SCF(Cdc4) (PubMed:12455686, PubMed:12101234). When associated with PCL9, may have a role in bud site selection in G1 phase (PubMed:9593297). PHO85 also phosphorylates the transcription factor SWI5 (PubMed:10692159). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Inhibited by the CDK inhibitor (CKI) PHO81 in response to phosphate starvation. Monomer. Forms a cyclin-CDK complex with at least 10 different cyclin partners: PCL1, PCL2, PHO80, CLG1, PCL5, PCL6, PCL7, PCL8, PCL9 and PCL10. Interacts with GLC8 and RIM15. Predominantly localizes to the nucleus. Phosphorylation of Tyr-18 seems to be important to discriminate between the different cyclin partners for binding. Increases GCN4 level. Present with 6160 molecules/cell in log phase SD medium. Belongs to the protein kinase superfamily. CMGC Ser/Thr protein kinase family. CDC2/CDKX subfamily.