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Interplay of Gene Expression Noise and Ultrasensitive Dynamics Affects Bacterial Operon Organization

Figure 4

Allolactose noise depends on transcriptional coupling in simulations of the E. coli lac operon.

A. Simplified reaction diagram of the model used. The complete reaction scheme and parameter values are given in Tables S7 and S8. Arrows depict flux arising from the mechanisms in the model. B. Predicted dynamics of allolactose (Alac) and permease (LacY) in excess inducer (extracellular lactose at 5,000 µM) are represented by 20 individual timecourses. C. Time correlation between permease and β-galactosidase (LacZ) for 100 timecourses. Error bars represent standard error of the mean. D. Coefficients of variation (CV = σ/μ, where σ is the standard deviation and μ is the mean) of metabolite allolactose at three extracellular lactose concentrations. E. CV of permease protein at three extracellular lactose concentrations. Bootstrapped mean and standard deviation of CVs (red bars in panels D and E) diverge from simulated CV when the distribution is highly skewed. Concentration 1.39 µM represents minimal induction of the lac operon; 83.0 µM represents mid-range induction; and 5,000 µM represents an excess of inducer with maximal lac operon induction. Error bars represent one standard deviation from bootstrap resampling.

Figure 4