Fig. 2
Effect of Rob on the mar operon input function. a Normalized input function (promoter activity in steady state relative to the maximum) as a function of the salicylate concentration for the wild-type (WT, blue) and ∆rob (red) strains. Open circles correspond to experimental data (error bars are standard deviations of three replicates), with input and output ranges of R in = 31.11 ± 2.46 and R out = 8.85 ± 0.04 (WT), and R in = 20.88 ± 1.17 and R out = 11.48 ± 1.03 (∆rob). Solid lines correspond to model predictions, with R in = 28.32 and R out = 6.77 (WT), and R in = 27.51 and R out = 7.17 (∆rob). Response fold change dependence on the fraction of functional MarR upon full induction (α parameter in the model, α ≈ 5%, Supplementary Table S1) is well predicted by the theory to be R out ≈ α −2/3 ≈ 7.4. b Both MarA activation strength and Rob concentration modulate the expression level of MarR in equilibrium (simulations for 5 mM salicylate). The effect or Rob becomes evident in a weak regime of MarA (natural system; dashed-dotted white line). The same scaling (≈ ρ 1/3) could be obtained if the action of MarA were strong, which would inactivate the effect of Rob (dotted white line). See text for details
