Figure 2.

Graphical solution of the equilibrium condition of Eq. (2) for varying steepness of the response function and varying relative degradation rates. The blue curves are graphs of r + α(1 - Z), the straight lines graph the degradation term γy. For intermediate values of γ the equilibrium concentration is close to θ and approaches θ when the response function steepness increases (red line), and there is active regulation. When γ is small, the basal transcription rate is sufficient to balance the degradation, and y* gets large (green line). When γ is large, degradation is so rapid that the protein concentration never reaches the level where it regulates. Maximal production is necessary to balance the degradation (magenta line).