Figure 1. Oligomerization of transcription factors (TF) and miRNAs induce thresholds in protein expression.

(A) Minimal model for protein synthesis including a miRNA. TF activate, with or without oligomerization of TF, the synthesis of a messenger RNA (RNA). This RNA can form an inhibitory complex, RNA_i, with a miRNA, which prevents it to encode the synthesis of the protein. We assume that the level of each component in the model can be controlled by synthesis and degradation. Steady-state levels of protein vs the level of TF are shown for different degrees of oligomerization of TF (n) in B, and for different rates of synthesis of miRNA (V _SMIRNA) in C. Horizontal red lines indicate an arbitrary threshold of protein needed to promote a cellular response. (D) Steady-state levels of protein vs V _SMIRNA for different rate constants of association between the RNA and the miRNA, k ₁. Parameter values used in the simulations are as in Table 2.