Binds GTP and exhibits intrinsic GTPase activity. May activate NF-kappa-B-mediated gene transcription. Promotes signal transduction through MTOR, activates RPS6KB1, and is a downstream target of the small GTPase-activating proteins TSC1 and TSC2 (By similarity). Interacts with MTOR. Belongs to the small GTPase superfamily. Rheb family.