Figure 3.

Gene expression noise randomizes the activation of the adaptive response. (A) Response activation time distributions are shown. Cumulative distributions show the percentage of cells that activated the adaptive response after MMS exposure. The activation time corresponds to the time when Ada levels crossed a threshold of 23 molecules per cell (a threshold close to the experimental detection limit). The experimentally measured distributions from time-lapse microscopy include between 59 and 149 cells for each MMS concentration (left). Model results are from 1000 independent Gillespie simulations for each MMS concentration (right). Identical data analysis was performed for simulated and experimental cell trajectories. (B) Shown is the average delay time between MMS addition and the generation of the first meAda molecule from 1000 simulated trajectories, conditional on the initial number of Ada molecules at the time of MMS addition. The red curve is for cells that initially had zero Ada molecules, the dotted black line is for one Ada molecule, the dashed black line is for two Ada molecules, and the solid black line is for more than two Ada molecules. The average waiting time between basal expression events is shown in gray. (C) Shown is the simulated distribution of response delay times after 2 mM MMS treatment for cells with initially zero Ada molecules (red) or more than two Ada molecules (gray). To see this figure in color, go online.