Characterization of TOR complex 2 (TORC2) in "Saccharomyces cerevisiae"

The TOR proteins play a central role in the control of cell growth. TOR proteins are the founding members of the phosphatidylinositol-related kinase (PIKK) family of protein kinases. In S. cerevisiae there are two TOR proteins, TOR1 and TOR2. TOR1 and TOR2 regulate cell growth via a rapamycin-sensitive pathway controlling translation, transcription, nutrient uptake, ribosome biogenesis and autophagy. TOR2 also has a unique, rapamycin-insensitive function, which is the control of the actin cytoskeleton. Recently, it has been found that the TOR proteins exist in two distinct complexes, TOR complex(TORC1) and TOR complex(TORC2). While TORC1 mediates the rapamycin-sensitive pathway, TORC2 is responsible for the control of the actin cytoskeleton. TORC1 comprises three proteins, TOR1 or TOR2, KOG1 and LST8. TORC2 consists of five proteins, TOR2, AVO1, AVO2, AVO3 and LST8. Thus, these structurally and functionally distinct TOR complexes account for the diversity of TOR signaling in yeast. Here we focused on the characterization of TORC2. Our studies suggest that TORC2 exists in an oligomeric state and that AVO1 and likely AVO3 act as scaffold proteins required for the integrity of TORC2. We also found that AVO1 plays a role as an adaptor protein mediating efficient phosphorylation of substrates. LST8 in turn appears to modulate TOR2 kinase activity possibly by binding directly to the TOR2 kinase domain. LST8 is common to both TORC1 and TORC2 and may therefore be important to respond to upstream signaling factors.