RAC1b,also named as TC25,belongs to the small GTPase superfamily and Rho family. RAC1 is a plasma membrane-associated small GTPase which cycles between active GTP-bound and inactive GDP-bound states. In its active state,it binds to a variety of effector proteins to regulate cellular responses such as secretory processes,phagocytosis of apoptotic cells,epithelial cell polarization and growth-factor induced formation of membrane ruffles.