Probably involved in the organization of the actin cytoskeleton by acting downstream of CDC42, inducing actin filament assembly. Alters CDC42-induced cell shape changes. In activated T-cells, may play a role in CDC42-mediated F-actin accumulation at the immunological synapse. May play a role in early contractile events in phagocytosis in macrophages (By similarity). Interacts with CDC42 (in GTP-bound form). Interacts weakly with RAC1 and not at all with RHOA (By similarity). The CRIB domain mediates interaction with CDC42. Belongs to the CDC42SE/SPEC family.