RAP1GAP, an 85/95kDa protein, is a member of a family of GAPs specific for Rap1. Though to be an important tumor suppressor, Rap1GAP has no sequence homology with other GAPs such as RasGAP, RanGAP and RhoGAP. Purified as a cytosolic and membrane-bound protein, both isoforms consist of two monomers each contain a dimerization and a catalytic domain. Mutations in the GAP domain of the tumor suppressor tuberin, can cause benign tumor phenotype tuberous sclerosis. There are 2 isoforms produced by alternative splicing.