Movie S2.

Time lapse images during fluorescence recovery after photobleaching of TMR-actin–labeled tactoid (2.64 μM actin, 1.5 mol % capping protein, and 5 mol % filamin) Initially, a tactoid a couple of microns in length is uniformly fluorescent. At t = 0 s, a portion of the tactoid’s fluorescent F-actin is irreversibly photobleached. Gradually, over hundreds of seconds, the photobleached portion of the tactoid becomes brighter as the remaining, unbleached, portion becomes darker, indicating diffusion of F-actin within the tactoid. Time is indicated in min:s.