Spatiotemporal Model of the Asymmetric Division Cycle of Caulobacter Cell

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1. DivJ-dependent phosphorylation of DivK is crucial for switching PleC from a phosphatase to a kinase

Figure 2.4: DivJ initiates the PleC phosphatase-to-kinase transition. For the full model, we plot signal-response curves (one-parameter bifurcation diagrams) for the steady state levels of (A) PleC kinase, (B) DivK~P, (C) PleD~P, and (D) DivK bound to PleC as functions of total DivJ (the parameter DivJ_tot in the model). Solid lines, stable steady states; dashed lines, unstable steady states. In our model, PleC_tot = constant = 1.0, but total DivK, total CtrA, and total PleD depends on DivJ_tot.

2. DivJ-dependent phosphorylation of DivK is crucial for switching PleC from a phosphatase to a kinase

Figure 2.5: Over-expressing DivK causes a drop in PleD phosphorylation. The steady state level of PleD~P is plotted against increasing amount of total DivK for (A) ΔdivJ divK_D53N, (B) ΔdivJ, and (C) wild type background. Although the absolute levels vary among the three cell types, in each case PleD~P level shows an initial increase followed by a drop at high DivK.

Figure 2.6: Over-expressing DivK causes activation the PleC switch independent of DivJ. (A) Two-parameter bifurcation diagram, indicating how the PleC switch behaves in cells expressing different levels of DivJ_tot and DivK_total (k_{syn_dk} is the rate constant for synthesis of DivK). PleC exhibits bistability within the crescent-shaped region bounded by the blue lines. (B) One-parameter bifurcation diagrams (signal-response curves) for three different values of k_{syn_dk}, indicated by the dashed hoizontal lines in panel A. Notice that PleC kinase level is always low if k_{syn_dk}<0.011 and always high if k_{syn_dk}>0.082.

3. The PleC-DivJ-DivK switch confers bistability to the DivL-CckA-CtrA module

Figure 2.7: The DivJ-PleC-DivK module controls the DivL-CckA-CtrA module. When the PleC switch is activated, DivK~P binds to DivL and inactivates components of the CckA module. One parameter bifurcation diagrams show the steady state levels of (A) DivL, (B) CckA kinase, (C) CtrA~P, and (D) CpdR~P as functions of DivJ_tot.