Figure 2.6.

Transcriptional time series for several different classes of rate constants. The schematic emphasizes two scenarios in which thermodynamic models of gene regulation are valid. In case 1, the promoter switches fast on the time scale defined by transcription initiation, while in case 2, the opposite limit is illustrated. In both limits, the steady-state number of transcripts (mRNA degrades due to the action of RNases and by dilution after cell division) is proportional to the fraction of time the promoter is in the active state (state 1), which can be computed using equilibrium techniques. We are grateful to Alvaro Sanchez for his articulation of the ideas embodied in this figure.