SPA-1 , signal-induced proliferation associated gene 1, encodes a 130 kDa protein (p130 SPA-1 ) with a domain related to Rap1 GTPase activating protein (Rap1GAP) at the N-terminus and to PDZ protein interaction domain followed by a leucine zipper motif at the C-terminus. It exhibits a specific GAP activity for Ras-related regulatory proteins Rap1 and Rap2, but not for other small GTPases. p130 SPA-1 was mostly localized at both the plasma membrane and the perinuclear membranous region co-localizing with Rap1 and Rap2. Expression of SPA-1 and rap1GAP genes tended to be segregate in various tissues, lymphoid and hematopoietic tissues expressing abundant SPA-1 transcript without rap1GAP , while those such as brain, kidney and pancreas exhibiting rap1GAP mRNA with little SPA-1 .Synonyms: GTPase-activating protein Spa-1, Signal-induced proliferation-associated protein 1, Sipa-1, Spa-1, p130 SPA-1