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Formins promote the elongation of preexisting filaments by removing barbed end capping proteins and forming a sleeve around the actin subunits. Formins are also capable of actin nucleation, a process which is spatiotemporally coupled with actin disassembly. Formins nucleate and polymerize actin filaments at focal adhesions at a rate of around 0.3 µm/min. Inhibiting formin protein expression results in a decreased filament elongation rate (0.1 µm/min), coupled with abnormal stress fiber morphology and an accumulation of actin binding proteins (e.g. α-actinin) Formins could, in theory, contribute to protrusive forces by remaining attached to the barbed end of actin filaments
