Appendix 1—figure 1. Model of formin function based on transitions between discrete states, as described in the text.

Unlike those of the main text, the schematics presented here only picture one actin protofilament for simplicity, without any implications for the model itself. In both panels, formin dissociation from states $O$ and $T$ is indicated by thick dark blue arrows. The FH1 domains, which lead to the formation of a ring complex that hampers this dissociation in profilin-associated states, is not explicitely represented here. (a) Simplified, no-profilin model introducing the notion of rapid equilibrium between monomer additions, and transit through a short-lived state $T$ upon monomer addition. (b) Model taking into account the association of profilin with the filament barbed end.