DIAPH3 (diaphanous homolog 3), also known as DIAP3, DRF3 or mDia2 of mouse origin, is a 1,193 amino acid member of the formin homology protein family and is required for the correct function of various cellular processes. DIAPH3 binds to both Profilin, a protein involved in cell maintenance, and to the GTP-bound form of Rho (Rho-GTP). Binding to both of these proteins allows DIAPH3 to recruit Profilin to the membrane, in a Rho-dependent manner. At the membrane, DIAPH3 promotes Actin polymerization and is required for stress fiber formation, cytokinesis and transcriptional activation of the serum response factor (SRF). DIAPH3 also regulates Actin dynamics by coupling Src tyrosine kinase (c-Src) and Rho during Actin signaling events. DIAPH3 contains one diaph-anous autoregulatory domain (DAD) and one Rho GTPase-binding domain (GBD). When DAD and GBD are intramolecularly bound, the GBD is occupied and DIAPH3 is inactive. Interruption of the DAD-GBD bond allows the GBD to bind to Rho-GTP, thus activating DIAPH3. Seven isoforms of DIAPH3 exist due to alternative splicing events.