Required for the assembly of F-actin structures, such as actin cables and stress fibers. Nucleates actin filaments. Binds to the barbed end of the actin filament and acts as leaky capper, slowing both polymerization and depolymerization. Protects the growing actin fiber from tight capping proteins and so increases the time of elongation and the total amount of F-actin. May organize microtubules by mediating spindle positioning and movement in the budding process. Potential target of the RHO family members. Homodimer, and possibly also homotetramer. Interacts with PFY1 via the FH1 domain and with actin via the FH2 domain. 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). Each FH2 dimer contains binding sites for 4 actin molecules. Present with 166 molecules/cell in log phase SD medium. Belongs to the formin homology family. BNI1 subfamily.