GDP dissociation inhibitors (GDIs) are proteins that regulate the GDP-GTP exchange reaction of members of the rab family. GDIs can bind and release GDP-bound Rab proteins from membranes. Two GDI proteins towards different Rab proteins have been identified. GDI1 interacts with almost all of the Rab proteins,while GDI2 interacts with Rabll but not Rab3A. GDI1 is expressed primarily in neural and sensory tissues and also in secretory cells,displaying a diffuse,cytoplasmic distribution in cells. It runs as a 55 kDa protein in SDS-PAGE.