Figure 10.

A) Probability densities of GFP molecules, for three versions of the O_RO_lac promoter model. Densities were generated by accumulating statistics in runs 250000 cell cycles in duration. (Solid line) Fully discrete model. (Dashed line) Fully continuous model. (Dash-dotted line) Hybrid model: the DNA binding states are represented by discrete variables, while all other species are continuous. All three methods produce virtually identical probability distributions. B) Probability density for species D₈, for the continuous model. The hybrid and fully discrete methods produce identical distributions in which D₈ spends 99.996% of the time at zero. This histogram shows that the continuous model artificially allows negative numbers (see inset time series).