Cdc12 formin accelerates dynamics and increases the bundle density in profilin-actin networks. (A) Time course of the spontaneous assembly of 5 μM Mg-ATP-actin monomers (10% pyrene labeled) in the presence of 15 μM SpPrf and the indicated concentrations of Cdc12. (B) The 95% F-actin polymerization time from (A) as a function of Cdc12 concentration. (C) Representative images of fluorescent (Alexa 488) phalloidin labeling of F-actin in networks forming via a spontaneous assembling of 5 μM Mg-ATP-actin, 1.2 μM α-actinin, and 15 μM SpPrf in the presence of varying concentrations of Cdc12. Polymerization is initiated at t = 0 s; scale bar = 30 μm. (D) The time to steady-state bundle density (open squares), steady-state S(q,t) (solid circles), and dynamic arrest (solid diamonds) as a function of Cdc12 concentration. (E) Steady-state linear bundle density as a function of Cdc12 concentration. (F) Average bundle intensity as a function of Cdc12 concentration.