RASAL1 is a member of the GAP1 family of GTPase-activating proteins. These proteins stimulate the GTPase activity of normal RAS p21 but not its oncogenic counterpart. Acting as a suppressor of RAS function, RASAL1 enhances the weak intrinsic GTPase activity of RAS proteins resulting in the inactive GDP-bound form of RAS, thereby allowing control of cellular proliferation and differentiation. This particular family member contains domains which are characteristic of the GAP1 subfamily of RasGAP proteins but, in contrast to the other GAP1 family members, RASAL1 is strongly and selectively expressed in endocrine tissues. Alternatively spliced transcript variants that encode different isoforms have been described [provided by RefSeq, Jul 2010] [taken from NCBI Entrez Gene (Gene ID: 8437)].