Protein kinase that positively regulates proper entry into stationary phase of cells under nutrient starvation conditions. Involved in glycogen and trehalose accumulation, derepression of stress-induced genes, induction of thermotolerance and starvation resistance, and proper G1 cell cycle arrest. Also involved in the activation of a meiotic genes activation pathway. Phosphorylates IGO1 and IGO2, both involved in the TORC1 control of gene expression and chronological life span. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Kinase activity is inhibited by phosphorylation by cAMP-dependent protein kinase (PKA). Interacts with the cyclin-dependent kinase (CDK) PHO85 and IGO1. Autophosphorylated. Phosphorylation by PKA strongly inhibits kinase activity. Phosphorylation by cyclin-CDK PHO80-PHO85 under favorable growth condition causes inactivation of RIM15 by promoting its export to the cytoplasm. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.