Binds GTP and exhibits intrinsic GTPase activity (By similarity). Activates the protein kinase activity of TORC1, and thereby plays a role in the regulation of apoptosis (PubMed:22493059). Stimulates the phosphorylation of S6K through activation of TORC1 signaling (PubMed:22493059). May also have a role in activating TORC2 signaling (PubMed:22493059). Belongs to the small GTPase superfamily. Rheb family.