Signal Induced Proliferation Associated Protein 1 (SIPA1)

SIPA1 is a mitogen induced GTPase activating protein (GAP). It exhibits a specific GAP activity for Ras-related regulatory proteins Rap1 and Rap2, but not for Ran or other small GTPases. This protein may also hamper mitogen-induced cell cycle progression when abnormally or prematurely expressed. It is localized to the perinuclear region. The protein contains a C-terminal leucine zipper motif and an N-terminal GTPase activating protein (GAP) domain homologous to the human RAP1GAP protein. Human and mouse Spa1 amino acid sequences are 90% identical, with their GAP domains 98% identical. Human SPA1 was expressed at high levels in lymphohematopoietic tissues and at lower levels in several other tissues. The authors noted that SPA1 and RAP1GAP appeared to have nearly segregate expression patterns.