Model based estimation of activity profile of p53. (a) Markov Chain Monte Carlo output for potential transcription factor activity profile values for first time series replicate at 4 hours (x axis) and 6 hours (y axis). (b) Concentration of p21WAF1 transcript determined by real-time polymerase chain reaction after addition of actinomycin D (10 μg/ml) to irradiated (5 Gy, 4 hours) MOLT4 cells cultured in RPMI. Expressed as percentage of initial concentration. (c) Using the degradation rate of p21WAF1 dramatically restricted the range of solutions to the Markov Chain Monte Carlo.