Histogram of the measured intervals superimposed with the probability density functions of the models. Distributions of intervals between consecutive transcription events for weak (left) and medium (right) inductions. Each bar is 180 s. Measurement time is 2 hours (measured every 60 s). (A) mean of measured intervals is 2233 s and standard deviation is 1506 s (data from 233 intervals extracted from 283 cells). (B) mean of measured intervals is 1433 s and standard deviation is 1243 s (data from 99 intervals extracted from 40 cells). The histograms of measured intervals are superimposed with probability density functions of models with 1, 2 and 3 steps that best fit the data. Dotted line: 1-step model, solid line: 2-step model and dashed line: 3-step model (partially covered by solid line).