Required for the assembly of F-actin structures, such as stress fibers. Depends on the Rho-ROCK cascade for its activity. Contributes to the coordination of microtubules with actin fibers and plays a role in cell elongation. Acts synergistically with ROCK1 to promote SRC-dependent non-apoptotic plasma membrane blebbing (By similarity). Self-associates via the FH2 domain. Binds to F-actin via its N-terminus. Binds to the cytoplasmic domain of CD21 via its C-terminus (By similarity). Interacts with ROCK1 in a Src-dependent manner (By similarity). Predominantly cytoplasmic. Regulated by intramolecular binding to a C-terminal auto-inhibitory domain. Effector binding abolishes this interaction and activates the protein (By similarity). The DAD domain regulates activation via by an autoinhibitory interaction with the GBD/FH3 domain. This autoinhibition is released upon competitive binding of an activated GTPase. The release of DAD allows the FH2 domain to then nucleate and elongate nonbranched actin filaments (By similarity). Phosphorylated by ROCK1. Belongs to the formin homology family.