mTOR (mammalian target of rapamycin, FK506 binding protein 12-rapamycin associated protein 1 (FRAP1)) is a 289 kD member of the PI3 kinase family, containing, HEAT, FRB, FATC domains. mTOR is expressed in the nucleus and cytoplasm and is a target for cell-cycle arrest and the immunosuppressive effects of FKBP12-rapamycin complex. mTOR controls ribosome biogenesis, cell growth, and acts as an ATP sensor. mTOR is repressed by nutrient deprivation and mitochondrial uncoupling. Association of raptor negatively regulates mTOR kinase activity, also inhibited by tuberin-hamartin tumor suppressor complex. mTOR is modified by phosphorylation and associates with FKBP12, rapamycin, p70 S6 kinase, 4E-BP1, raptor, CLIP-170, tuberin, and hamartin. The Poly6199 antibody recognizes human mTOR and has been shown to be useful for Western blotting.