Cortactin is required for enhanced turnover of Arp3B. (A) The immunoblot shows the level of cortactin in HeLa cells treated with cortactin siRNA. (B) The immunoblot shows the expression level of RNAi-resistant GFP-tagged Arp3 and Arp3B in HeLa cells treated Arp3/Arp3B and cortactin siRNA. (C) Immunofluorescent images showing representative actin tails visualized with Alexa Fluor 568 phalloidin (magenta) in cells expressing GFP-tagged Arp3 and Arp3B (green) and treated with the indicated siRNA. Scale bar = 5 µm. (D) Immunoblot analysis of the level of cortactin in HeLa cells stably expressing GFP^PA-tagged Arp3 (blue) and Arp3B (red) and treated with cortactin siRNA. (E) Quantification of the half-life of photoactivated GFP^PA-tagged Arp3 or Arp3B in actin tails in cells treated with cortactin siRNA. The graph represents the best-fitting curve for each condition (continuous line), together with the average normalized intensity of the GFP signal at every time point (error bars represent the SEM for the indicated number of tails).