Inferring Biological Mechanisms by Data-Based Mathematical Modelling: Compartment-Specific Gene Activation during Sporulation in Bacillus subtilis as a Test Case

Figure 4

The 𝜎^𝐹 response as an ultrasensitive response. (a) The phosphorylation and dephosphorylation reactions of AA by AB and IIE, respectively, enable an ultrasensitive response. (b) The fraction of IIE that is bound in IIE/AA-P complexes over time. (c) The rate of AA-P dephosphorylation (blue line) is lower than the rate of AA phosphorylation (green line) until septation (time 𝑡=0). (d) The relative rate of AA-P dephosphorylation and AA phosphorylation (blue line) is close to but below 1 until septation (𝑡=0). The stronger increase in the rate of AA-P dephosphorylation then leads to the accumulation of free 𝜎^𝐹 and binding to the RNA holoenzyme (green line). Septation (a 4-fold increase in the IIE concentration) takes place at time 𝑡=0 in all panels.

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