Figure 5. Negative feedback amplifies expression noise in the sequestration model.

(A)–(C). Fano factor of mRNA, miRNA and protein are plotted versus α_m. Solid lines represent the simulation results and dashed lines represent the analytical calculation from the mean field model. The mean field model cannot be used to describe the system around the threshold, where the mRNA and miRNA levels are comparable. The solid straight line in (C) represents the asymptote for protein Fano factor value for large α_m. (D). Histogram protein numbers at steady state for α_m = 1.0: the mean values are 〈p〉 = 600, $\frac{\delta p^2}{\langle p\rangle }=43.2$. The protein distribution shows a long tail, which suggests that while mean values may be kept low, protein numbers can exhibit large values across the population allowing the transcription factor to act at promoters with widely different sensitivities.