Fig. 4.
Dependence on the motor density. By varying the motor density σm on the surface, the feedback between growth, and the fluctuations that arise in the motility assay can be examined. In general high motor densities lead to less fluctuations and a more persistent movement as can be seen in the time overlay image in (B), σm = 700 nM, while low motor densities lead to a more fluctuations (A), σm = 30 nM. The higher the noise level (i.e., the lower σm) the higher is the chance for individual strings to cross their own tail and to form closed rings. The increased probability for ring closure events is directly reflected by the higher abundance of closed rings at low motor densities quantified by the ratio of open to closed rings Γ (C). The radial distribution of closed rings itself is unaffected as can be seen in the decay lengths ld of the exponentially decaying distributions (D). By contrast, the frozen-in curvature of the open rings directly reflects the fluctuations and the persistence of the movement in the motility assay: here ld monotonically increases with increasing motor concentration σm. The actin concentration was set to ρ = 3 μM and the fascin concentration was c = 0.2 μM. All scale bars are 50 μm.