Comparison of mTOR and CDK9 complexes. mTOR is largely cytoplasmic, whereas CDK9 is found in both compartments. To reduce complexity, only the most salient cofactors are shown. mLST8 and RAPTOR interact with mTOR to form mTORC1 and separately with CDK9 to form CTORC1. Although the composition is very similar, the functions of these 2 complexes are distinct, with mTORC1 acting in translation in the cytoplasm and CTORC1 acting in transcription in the nucleus. mLST8 and RICTOR interact with mTOR to form mTORC2 and with CDK9 to form CTORC2. Again, these complexes have different functions, with CTORC2 modifying the overall ribosome profile, whereas mTORC2 is not considered to act in translation.