Fig. 2.

Binding of Arp2/3 complexes to filaments is enhanced by VCA. (A) Preassembled, immobilized, fluorescent actin filaments (Left) bound Arp2/3-SNAP549 molecules (10 nM) in the presence of 1 µM G-actin, 300 nM VCA, and 20 nM capping protein. Locations of all Arp2/3 complex binding events recorded over 15 min are plotted (heat map; marker color reflects local density: cyan <10; blue 10–19; green 20–29; orange 30–39; and magenta >39 events within a 0.4-μm radius). Locations where >9 neighboring events occurred (Right; red) correspond closely with filament locations (green traces). (Scale bar: 2 μm.) (B) Fraction of filament segments (0.4 µm in length) that had bound at least one Arp2/3 complex at or before the indicated time (total of 113 and 105 segments with and without VCA). Data are corrected for background (Materials and Methods). Envelopes: 90% confidence intervals. Smooth curves were calculated from exponential fits (Materials and Methods).