Fig 1. Emergence of multi-modality due to SPK.

(a) A diagram of a self-repressing gene, where ε is a parameter that multiplies the kinetic rates of all gene reactions (b) The stationary PMF for different ε which is showing transition from fast promoter kinetics, i.e., ε → ∞, to SPK, i.e., ε → 0, in a non-cooperative self-repressing gene. The stationary PMF is bimodal for small ε and unimodal for large ε. The deterministic equilibrium coincides with the fast kinetics mode. Refer to S1 Text §6.1. (c) A diagram of a repression-activation two-node network. (d) SPK gives rise to four modes while the deterministic model admits a unique stable equilibrium which is marked as a white point, refer to S1 Text §6.2. The surface is plotted using (10).