These two TOR activities have been linked to two distinct protein complexes, TORC1 and TORC2 (Loewith et al. 2002). Each has a sister complex in mammalian cells (Hara et al. 2002; Kim et al. 2002; Nojima et al. 2003; Sarbassov et al. 2004). TORC1 is comprised of yeast TOR1 or TOR2, LST8, and KOG1; the mammalian orthologues comprising mTORC1 are mTOR, Gftl/mLST8, and Raptor. Raptor/KOG1 functions in TORC1 to recruit substrates for phos-phorylation by TOR (Hara et al. 2002; Kim et al. 2002; Nojima et al. 2003). Rapamycin-FKBP12 complexes specifically disrupt TORC1 activity, perhaps by dislodging Raptor from TOR (Oshiro et al. 2004). Nutrient stress may reduce TORC1 activity by increasing the strength of the Raptor-TOR interaction, thus inhibiting Raptor's ability to recruit substrates for phosphorylation by TOR (Hara et al. 2002).
TORC2 is comprised of TOR2, LST8, AVO1, AVO3 (Loewith et al. 2002; Wullschleger et al. 2005), and a few yeast-specific proteins (Reinke et al. 2004); the mammalian orthologues in mTORC2 are mTOR, mLST8, hSin1 and Ric-
tor (Sarbassov et al. 2004; Yang et al. 2006). TORC2 regulates the cytoskeleton in both yeast and mammals (Helliwell et al. 1998; Jacinto et al. 2004; Kamada et al. 2005; Wullschleger et al. 2005).
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