Fascin-induced actin filament bundling slows down the recruitment of cofilin. (A) 10% Alexa-488 labeled actin filaments, grown and aged for 15 min from surface-anchored seeds, in the absence or presence of 200 nM human-fascin1, in a buffer containing 0.2% methylcellulose, are subsequently exposed to 80 nM mCherry-cofilin1 at time 0 (see Materials and methods). (B) Fluorescence images showing the different channels from the white box shown in A, in the presence of fascin. (C) Fluorescence intensity of bound cofilin, normalized by the amount of F-actin, as a function of time. Both curves increase roughly linearly. Linear fitting indicates that cofilin binding to single actin filaments is 15 times faster than on fascin-induced actin filament bundles (N = 3 independent experiments). Shaded areas represent SD.