Computer simulations with F-actin lattice site competition reproduce ring kinetics and rupture events of cyk-1(RNAi). (A) Four modeled ring components: actin (white), myosin (green), plastin (red) and β-heavy-spectrin (cyan). (B and C) Snapshots of ring formation simulations at the beginning of simulation (left), the time of ring formation (middle) and the end of simulation, for control (B) and fragilized networks (C). (D) 2D cross-section simulation of ring constriction. Inset: zoom view of ring section. (E) Series of superimposed snapshots showing a discontinuity in the ring during constriction of a fragilized ring. Images at 10-s intervals. Myosin motors are not shown; see Video 4. (F) Percentage of simulations where rings fail to constrict (40 simulations were analyzed per condition). (G) Measured constriction rates for each simulated case that did not break during constriction.