Fig 4. Prediction of mRNA variance as a function of mean, when the promoters share TFs with other competitor sites.

(A) Schematic of a single target promoter sharing TFs with multiple competitor sites. (B) The variance of mRNA molecules per promoter (var(m)/N_P) versus the mean per promoter (〈m〉/N_P), when the TFs act as activators. (C) The mRNA variance per promoter versus mean per promoter when the TFs act as repressors. In both the subfigures B and C, different numerical data points are obtained for various numbers of competitor sites by varying the TF copy number. Note that all the data for a single target promoter collapse onto a master curve (black curve). Data for a single target promoter is shown by closed symbols, and the data for two target promoters are shown by open symbols. The parameters related to the promoters (k_on, k_off, r, γ) are taken from the Table 1, while the number of competitor sites are systematically varied and listed in the figures. The master curves are predictions from Eq 3.