Fig. 4.
The effects of the AbrB–Rok module on the competence switch and the sporulation timer. (A) We show the level of AbrB and RoK as function of Spo0A* that is an inhibitor of AbrB. Spo0A* concentration exceeds the threshold level S1 and lead to a decrease in the AbrB concentration and consequently to an increase in the concentration of Rok that is inhibited by AbrB. Both AbrB and Rok acts as transcription inhibitors of the competence regulator ComK. Hence the competence window is determined by x, the combined concentration of AbrB and Rok, which has low values between S1 and S2. The effect of the reduction of x is an increase in the level of ComKveg (the vegetative ComK concentration) and consequently increase in the switching rate τ−1. (B) We show the dynamical behaviors of Spo0F, Spo0A, and Spo0A* as function of time for constant stress level. We note that the increase in the growth rate of Spo0F is the outcome of the increased level of Spo0A*, which acts as an up-regulator of Spo0F (via σH).