Illustration of the counting mechanism. The steady state is shown. (solid grey: stable steady state; dotted grey: unstable steady state. p4 = 0.002). The corresponding values of the steady state are shown as indicated in Figure 2C (0.008, 0.050, 0.328 μM from bottom to top). Dotted blue arrows indicate the equilibrium concentrations. The threshold level is indicated at the text box. Solid black arrows represent the Bax concentration reached during each pulse of p53. Temporal responses of oligomerized Bax (solid red) and PUMA (dashed violet) are shown.