GDP-dissociation inhibitor preventing the GDP to GTP exchange of most Rab proteins. By keeping these small GTPases in their inactive GDP-bound form regulates intracellular membrane trafficking. Negatively regulates protein transport to the cilium and ciliogenesis through the inhibition of RAB8A. Interacts with RHOH. Interacts with the GDP-bound forms of RAB3A, RAB3B, RAB3C, RAB5A, RAB5B, RAB5C, RAB8B, RAB10, RAB12, RAB35, and RAB43; binds RAB3D to a lesser extent. Interacts with RAB8A (GDP-bound inactive form); prevents RAB8A activation. Interacts with DZIP1; negatively regulates the interaction of GDI2 with GDP-bound RAB8A. Ubiquitously expressed. Belongs to the Rab GDI family. Was originally thought to originate from mouse.