TOR (Target of Rapamycin) is a Ser/Thr kinase that was originally identified by genetic screening using the budding yeast Saccharomyces cerevisiae. The TOR protein forms two structurally and functionally distinct complexes (TOR complex 1, TORC1, and TOR complex 2, TORC2). TORC1 is involved in various cellular activities, such as cell growth, ribosome biogenesis, translation initiation, metabolism, stress response, aging, and autophagy. TORC2 is involved in actin organization, sphingolipid biogenesis, and endocytosis. TORC1 plays a central role in the signaling network in response to stimuli coupled to internal and external nutrient conditions, particularly an amino acid sufficiency. A dimeric complex of Rag GTPases, the activity of which is regulated by the guanine nucleotide-loading status, and some regulator proteins communicating with Rag GTPases are involved in the activation of TORC1 by amino acids. In TORC2 signaling, membrane stress appears to be a cue, in which some proteins associated with respective membrane compartments, such as eisosomes, play a role.
Part of the book: The Yeast Role in Medical Applications