Kinetics of gene induction. (A) Two mechanisms which underlie the kinetics of gene induction are sequential activation of TFs and mRNA stability. While much research attention was given to the former, the latter was overlooked by many studies. Both mechanisms act in cells in parallel, and thus, the observed dynamics of transcriptional response reflects their superposition. (In the cartoon, waves 1, 2 and 3 refer to early-, intermediate- and late- kinetic responses.) (B) The standard kinetic model predicts that the rapidity of a transition between former and new transcript steady states is determined by the transcript's stability (T1/2 = ln2/α). The figure shows simulated kinetic response of four mRNAs with the same transcription rate (β = 5) and different degradation rates (blue: α = 2.0; green: α = 1.0; red: α = 0.5; black: α = 0.2). A pulse stimulation was exerted at t = 0 and terminated at t = 5. Note that upon induction, the most unstable mRNA (blue, highest α) reaches the lowest steady-state level, but it does so very rapidly (lowest T1/2). (C) Transcription rates of the four mRNAs were adjusted to bring them to the same level at t = 5.