Formin proteins are potent regulators of the actin cytoskeleton, serving as nucleation and elongation factors for actin filaments. Formins are large (120-220 kDa) multi-domain proteins characterized by a formin homology 2 (FH2) domain, which mediates interactions with actin.

Many formins also contain an N-terminal autoinhibitory domain, which inactivates the FH2 domain. Rho GTPases can activate many autoinhibited formins, releasing the FH2 domain to allow actin binding and filament nucleation.

Structural studies of full-length formins and formin-actin complexes are underway to understand the mechanisms of autoinhibition and actin filament nucleation.