Significance RAS proteins control many aspects of cellular biology in response to extracellular stimuli. These essential nodes of signal transduction interact with effector proteins that contain conserved RAS-binding domains. Mutations in RAS proteins are a common cause of cancer; hence, understanding the function of their downstream effectors is important for the development of novel therapies. In this study, we characterize the interaction between RAS and the effector protein Sin1, a critical component of the mTORC2, through biochemical and structural approaches. We discover that Sin1 contains an atypical RAS-binding domain and assess the role of this interaction in cells and mice. Moreover, we find that this interaction is dispensable for mTORC2 activity and assembly, suggesting an alternative function for Sin1 in cells.