Noise in wild type HipBA toxin-antitoxin system. (A) Total HipA concentration in a single simulated cell over time. Note the strong correlation with (B), the total HipB concentration. (C) The ratio of free (unbound) HipA to free HipB plus free HipA. The quantity is defined as R. A value of R exceeding 0.5 indicates persistence, shown with a dashed line. Plot shows stochastic data from several simulated cells (gray) and one persistence event (black). The black trace corresponds to the HipA and HipB plots in (A) and (B). (D) Histogram showing distributions of R.