Regulates the GDP/GTP exchange reaction of the Rho proteins by inhibiting the dissociation of GDP from them, and the subsequent binding of GTP to them (PubMed:8356058, PubMed:7512369). Regulates reorganization of the actin cytoskeleton mediated by Rho family members (PubMed:8262133). Interacts with RHOA (PubMed:20400958). Interacts with RAC1 (PubMed:7512369). Interacts with RAC2 (PubMed:10655614). Interacts with CDC42 (PubMed:7512369). Detected in bone marrow, thymus and spleen. Belongs to the Rho GDI family.