FIG 5.

Schematic of the mathematical model of TCS signaling with cross talk. (a) Architecture of the generalized mathematical model. The input I_i is detected by HK_i, which gets phosphorylated (HK_i with a yellow dot) and then transfers the phosphoryl group either to the cognate response regulator, RR_i (blue), or to the noncognate response regulator (RR_j,$j\ne i$[green]). Activated RRs trigger downstream gene expression via promoter P_i. Inactive HKs can act as phosphatases, which dephosphorylate active RRs. (b) Sample interaction matrix for N = 4. The diagonal positions represent cognate interactions, and the nondiagonal positions represent noncognate interactions. Zeros in the nondiagonal cells represent the absence of the corresponding cross talk interactions. The ratio of the efficiencies of phosphotransfer to noncognate and cognate interactions is γ. 2^N(N–1) such interaction matrices are possible depending on whether each nondiagonal entry is zero or not.