Cortactin stabilizes ADP-Arp2/3 complex branch junctions and favors renucleation. (A) Debranching rates for different pulling forces for ADP (yellow)- or ADP-BeFx (medium gold)-Arp2/3 complex branch junctions in the presence of 20 nM cortactin, and various actin concentrations. Each data point is from a single experiment with at least 60 and 37 analyzed branches for ADP- and ADP-BeFx-Arp2/3 complexes, respectively. Error bars are standard deviations. The dashed line for the ADP-BeFx-Arp2/3 complex in the presence of cortactin is a single-exponential fit from the data. (B) Branch renucleation ratio for different pulling forces for ADP-Arp2/3 complex branch junctions, in the presence (yellow) of 20 nM cortactin, with 1.5 μM G-actin and 0.2 mM ATP. Each point is from a single experiment from at least n = 30 branches. Error bars are standard deviations. In A and B, yellow lines are best fits of the data, obtained by the simultaneous error minimization of the probability of renucleating a branch and of the debranching rate, for ADP-Arp2/3 complex with cortactin, and debranching rates and renucleation ratios in the absence of cortactin are shown as lines, as in Fig. 3 (ADP (blue)- and ADP-BeFx (green)-Arp2/3 complex branches), for comparison.