Movie S1.

Spontaneous SFSS. Two color confocal time-lapse movie and kymographs corresponding to the cell in Fig. 1D and E showing a spontaneous SFSS developing. Actin is depicted in green (left) and Zyxin in magenta (middle) and movie on right is merged colors. Animated kymographs are shown for each channel. Red line at beginning of movie indicates the stress fiber from which the kymographs were generated. Flashing white box in middle of move indicates time zero of SFSS formation, when zyxin begins to accumulate and actin thins further. White arrow in the merged movie denotes the SFSS. Time interval between the beginnings of exposures is 2 seconds.