Figure 3

miRNA-mediated self-loops can keep the host gene expression robustly in a ON-state. (A) Schematic representation of a transient drop of the input TF q of duration T^∗(time is in protein half-life units τ _p ) (B) Response of the three circuits to the temporary absence of signal depicted in A. The iMSL response (red line) is a slow protein concentration decrease, followed by a quick recovery of the ON-steady-state when the fluctuation is over. For a tSL (orange line) or a sTF (blue line) the switch-off dynamics is just due to mRNA and protein degradation. Even if the transcriptional negative feedback can accelerate the recovery, the distance d from the ON steady state that is reached by the target protein level during the temporary absence of the input activator is determined by the switch-off response. (C) The distance d from the ON steady-state reached by the target level is plotted as a function of the duration of the TF q absence (d = 1 when the protein level reaches zero). The iMSL circuit (red line) requires a more persistent absence of signal to show a significative reduction of the host protein product level with respect to the tSL or the sTF (blue line). The parameter values are the same of Figure2, with comparable mRNA and miRNA stability (τ _r /τ _s = 1).