Movie S5.

Liquid bundles exhibit Rayleigh–Plateau like instabilities. Initially (t < 0 s), F-actin (2.64 μM actin and 0.5 mol % capping protein) is crowded to the surface. At t = 0 s, filamin cross-links (10 mol %) are introduced and rapidly (<1 min) mediate F-actin assembly into bundles. Bundles coalesce into one long (>10 μm) bundle. The fluctuations in fluorescence intensity indicate fluctuations in F-actin density along the bundle. These fluctuations slowly evolve over several minutes into chains of periodically spaced, tactoid shaped bulges, joined by thin bridges of actin, reminiscent of a column of liquid with capillary or Rayleigh–Plateau instabilities. The fluorescence intensity is normalized for each frame individually for the clarity of presentation. Time is in min:s.