Figure 2.

An optimal level of basal signaling results in fast responses to appropriate stimuli without spurious “noise-induced” activation. The product of the probability of activation when cognate ligand is present and the probability of not being activated without ligand (within an observation time) is graphed as a function of basal signaling level. The parameters are k₁=320, δ=2600, k₂=10, N=6, and the observation time is 5 s. Figs. S8–S9 (Ref. ¹⁵) show that this qualitative result is robust to changes in these parameters.