Steady state signal-response curves for the various TCS modules.

<p>Each plot shows the steady state levels of the phosphorylated RR in the y axis at different values of the signal k₁ (SK autophosphorylation rate constant) or k₂ (SKP dephosphorylation rate constant) in the x axis. When the signal modulates SK dephosphorylation (changes in k₂), the system behaves symmetrically to when SK phosphorylation (changes in k₁) is modulated. In the first case, increases in signal intensity cause the fraction of RRP to decrease, while in the latter, increases in signal intensity cause the fraction of RRP to increase. A, C, E: Response curves of TCS modules with monofunctional sensor. B, D, F: Response curves of TCS modules with bifunctional sensor. A, B, Response curves of Model A. C, D: Mathematically controlled comparison between the response curves of Model B and those of Model A. E, F: Mathematically controlled comparison between the response curves of Model C and those of Model A. Mathematical controls are implemented to make sure that the differences in response between the alternative modules are due to the presence of third component and not to other spurious differences.