Essential 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. LST8 is involved in the negative regulation of transcription factors GLN3 and RTG1-RTG3, limiting the synthesis of alpha-ketoglutarate, glutamate and glutamine. LST8 is required for targeting of amino acid permeases (AAPs) to the plasma membrane. 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. LST8 is involved in maintenance of cell wall integrity. LST8 modulates TOR2 kinase activity. The target of rapamycin complex 1 (TORC1) is composed of at least KOG1, LST8, TCO89 and either TOR1 (TORC1-A) or TOR2 (TORC1-B) (PubMed:12408816, PubMed:12631735, PubMed:12719473). TORC1 binds to and is inhibited by FKBP-rapamycin (PubMed:12408816). Interacts with PIB2; following activation of PIB2 by glutamine or cysteine and as part of the TORC1 complex (PubMed:29698392). The target of rapamycin complex 2 (TORC2) is composed of at least AVO1, AVO2, BIT61, LST8, TOR2 and TSC11 (PubMed:12408816, PubMed:12631735, PubMed:12719473). TORC2 likely forms a homodimer (PubMed:16002396). Contrary to TORC1, TORC2 does not bind to and is not sensitive to FKBP-rapamycin (PubMed:12408816). LST8 binds to the C-terminal kinase domain in TOR2 (PubMed:16002396). Also localizes to membranous structures both proximal to, yet distinct from, the plasma membrane as well as within the cell interior, probably endosomal or Golgi membranes. Present with 589 molecules/cell in log phase SD medium. Belongs to the WD repeat LST8 family.