FIGURE 6.

Reversibility of disorder-order transitions in the actin myosin system. Actin concentration is 2.4 μM with an average of 50 myosin minifilaments per actin filament. (A) In the presence of ATP, i.e., motor activity, the system stays disordered. (B) Self-assembly is observed when initial ATP is exhausted (90 min). (C) ATP is reintroduced through UV-activated caged-ATP molecules. Self-assembled structures are disrupted in 2–3 min and the system returns to a disordered state. (D) Self-assembly is again observed when reintroduced ATP is subsequently exhausted (180 min). (Diagram) Illustrated schematic for instability-driven switch between dynamic disorder and ordered actomyosin architectures. Free actin filaments are indicated in green, actin filaments incorporated into a cluster in black, active myosin II minifilaments in red, and inactive myosin II minifilament in blue. (Scale bar is 20 μm.)