Guanine nucleotide exchange factor (GEF) for Rho and Rac. GEF proteins activate small GTPases by exchanging bound GDP for free GTP (PubMed:18396277). Along with DOCK1, mediates CRK/CRKL regulation of epithelial and endothelial cell spreading and migration on type IV collagen (By similarity). Interacts with CRK and CRKL. Associated with the edge of the plasma membrane in intestinal epithelial cells spreading on type IV collagen. Highly expressed in lens, where it predominantly localizes to anterior epithelial cells, and is weakly expressed in lens fiber (at protein level). Expressed in brain, eye, lung, spleen and kidney, but not in thymus or peripheral blood leukocytes. In the lens, expressed from 15.5 dpc to maturity. The DOCKER domain may mediate some GEF activity. Defects in Dock5 are the cause of rupture of lens cataract. It affects both eyes and is inherited as an autosomal recessive trait. Homozygotes spontaneously develop opacity of the lens at 35-60 days of age. The initial pathological changes appear at about 35 days of age in the deep layer of the posterior cortex as irregular swelling, condensation, degeneration and fragmentation of the lens fibers, leading to rupture of the lens capsule at the posterior pole at 45-100 days of age. Following rupture, the lens nucleus becomes dislocated behind the lens or occasionally in the anterior chamber. Belongs to the DOCK family.