Actin nucleation and elongation factor required for the assembly of F-actin structures, such as actin cables and stress fibers (PubMed:10678165, PubMed:23558171). Required for cytokinesis, stress fiber formation and transcriptional activation of the serum response factor (PubMed:10678165, PubMed:23558171). Binds to GTP-bound form of Rho and to profilin: acts in a Rho-dependent manner to recruit profilin to the membrane, where it promotes actin polymerization (PubMed:10678165). DFR proteins couple Rho and Src tyrosine kinase during signaling and the regulation of actin dynamics (PubMed:10678165). Also acts as an actin nucleation and elongation factor in the nucleus by promoting nuclear actin polymerization inside the nucleus to drive serum-dependent SRF-MRTFA activity (PubMed:23558171). During mitosis, co-localizes with the actin-rich cleavage furrow and with the microtubule-rich central spindle during cytokinesis (By similarity). Shuttles between the cytoplasm and the nucleus (PubMed:19117945). Increased expression in S phase and mitotic cells; levels decrease as cells enter in G0/G1 phase due to proteasomal degradation (at protein level). The DAD domain regulates activation via by an autoinhibitory interaction with the GBD/FH3 domain (PubMed:23558171). This autoinhibition is released upon competitive binding of an activated GTPase (PubMed:23558171). The release of DAD allows the FH2 domain to then nucleate and elongate nonbranched actin filaments (PubMed:23558171). Ubiquitinated. Belongs to the formin homology family. Diaphanous subfamily.