Arp3B reduces the stability of actin networks. (A) Image stills from Video 2 and Video 3 at the indicated times in seconds before and after photoactivation showing the movement of YFP-tagged virus (yellow arrow) in HeLa cells stably expressing Cherry-GFP^PA-β-actin (magenta, before photoactivation) in control and Arp3B RNAi–treated cells. The white arrow indicates the position of photoactivated Cherry-GFP^PA-β-actin at time 0 (green). (B) Quantification of the half-life of photoactivated GFP^PA-β-actin in actin tails in Arp3B RNAi–treated cells. These data were collected at same time as the data in Fig. 9 D. (C) Image stills from Video 4 and Video 5 at the indicated times in seconds showing the movement of YFP-tagged virus (yellow arrow) in HeLa cells stably expressing LifeAct-RFP (shown in magenta) together with GFP^PA-tagged Arp3 or Arp3B. White arrows indicate the position of photoactivation of GFP^PA-tagged Arp3 or Arp3B at time 0 (green). (D) Quantification of the half-life of Arp3 and Arp3B in actin tails after activation of the GFP^PA tag. For B and D, the left graphs represent 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). The right graphs show the mean half-life and SEM from n = 3 independent experiments. Student’s t test was used to determine statistical significance; **, P < 0.01. Scale bars = 2.5 µm.