Phosphatidylinositol 3-kinase homolog, component of both TORC1 and TORC2. TORC1 regulates multiple cellular processes to control cell growth in response to environmental signals. Nutrient limitation and environmental stress signals cause inactivation of TORC1. Active TORC1 positively controls ribosome biogenesis via control of rRNA, ribosomal protein and tRNA gene expression, and rRNA processing. TORC1 positively controls protein biosynthesis by regulation of mRNA stability, translation initiation factor activity, and high-affinity amino acid permeases that serve to provide amino acids for use by the translation machinery. TORC1 also promotes growth by sequestering a number of nutrient and general stress-responsive transcription factors in the cytoplasm. TORC1 negatively controls macroautophagy, a process to recycle surplus cytoplasmic mass under nutrient starvation conditions. TORC1 controls many of these processes via TIP41-TAP42-mediated inhibition of the type 2A-related phosphatases PP2A and SIT4. In nutrient rich conditions, responsible for the phosphorylation of AGC S6 kinase (S6K) YPK3, activating YPK3 kinase activity and promoting phosphorylation of ribosomal protein S6. Phosphorylates kinase SCH9 at 6 amino acids in the C-terminus, activating SCH9 kinase activity to properly regulate ribosome biogenesis, translation initiation, and entry into stationary phase. TORC2 regulates cell cycle-dependent polarization of the actin-cytoskeleton, cell wall integrity, and receptor endocytosis. TORC2 controls polarity of the actin cytoskeleton, which is required for orienting the secretory pathway toward discrete growth sites, via the RHO1/PKC1/MAPK cell integrity pathway by activating the RHO1 guanine nucleotide exchange factor ROM2. TORC2 phosphorylates the AGC kinase YPK2, an upstream effector of the cell integrity pathway. TORC2 negatively regulates calcineurin-dependent stress signaling via phosphorylation of its effector SLM1-SLM2.
