Figure 1.

A simplified model for a treadmilling motor system. The thickness of the arrows at each end of the filament is proportional to the polymerization and depolymerization rates which are used in the simulation with the realistic parameters (Fig. 2A). In our model, we start with the filament consisting of ATP subunits (the first panel). As time passes, the slow end tends to have ADP subunits because of the ATPase in the filament and the polarity in the dynamics. At the steady-state (the latter two panels), the filament of the actin-like treadmilling motor moves toward the fast end without changing its length by polymerization at the fast end and depolymerization at the slow end.