p53 dynamics. A: Time dependence of the p53 concentration after application of different cellular stresses at time zero. B-D: The colors show peak concentration of free p53, after the system has settled into a steady-state or stable oscillations (note that the peak level differs from the average only when there are oscillations), as a function of two model parameters. The white line marks where the spikyness (amplitude/average ) of p53 oscillations becomes equal to 2 (i.e., where the amplitude becomes twice the average). Thus, spiky oscillations occur to the right of the line in (B) and (D), and to the left in (C). The white dot shows the parameters corresponding to the default resting state (see Table 1). Black arrows illustrate the change in parameters we impose on the system to model the respective stresses.