Plays an essential role in the proliferation of yeast cells. Involved in a signaling pathway, required for optimal cell wall integrity, that acts in parallel with the PKC1-SLT2-dependent pathway. Downstream kinase in the sphingolipid-mediated signaling pathway. Its phosphorylation is regulated by the intracellular sphingolipid concentration. Cooperates with SLI1 in mediating resistance to the sphingolipid biosynthesis inhibitor drug myriocin (ISP-1). Its kinase activity is essential for the resistance. Required for both receptor-mediated and fluid-phase endocytosis, but is not necessary for receptor phosphorylation or ubiquitination. Necessary for the internalization of plasma membrane proteins carrying different types of internalization signals. Acts downstream of the PKH kinases to control endocytosis by phosphorylating components of the endocytic machinery. Phosphorylation of residue Thr-504 in the activation loop is essential for activity. phosphorylates and down-regulates flippase activator FPK1. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by phytosphingosine (PHS), a sphingoid long chain base. Activated by PKH1 phosphorylation. Intracellular localization is regulated by the intracellular sphingolipid levels. During the yeast cell cycle, distributed both on the plasma membrane and in the cytosol. Greater accumulation was detected on the plasma membrane, such as in the budding area, a daughter cell and the neck region of the mother cell in the S phase, and the septum between a mother cell and a daughter cell in the G2 phase. Autophosphorylated. Autophosphorylation is stimulated by PHS. Phosphorylated by PKH1. PHS stimulates phosphorylation by PKH1. The N-terminal half is phosphorylated by FPK1. Present with 2950 molecules/cell in log phase SD medium. Belongs to the protein kinase superfamily. AGC Ser/Thr protein kinase family. RAC subfamily.