Fragility of bistability.

<p>(A) Histograms of monomer concentration <i>x</i> as a function of control parameter <i>B</i> (from 3.4 to 3.9 in steps of 0.1) with other parameters chosen as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0121681#pone.0121681.g004" target="_blank">Fig 4D</a>. (B) Radial pair-correlation function for <i>D</i> = 3 (<i>X</i>) and 1 (<i>X</i>₂) (dashed black line) and <i>D</i> = 0.3 (<i>X</i>) and 0.1 (<i>X</i>₂) (solid black line) compared with random distribution (red line; see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0121681#sec010" target="_blank">Material and Methods</a> for details). (C) Range of <i>B</i> values with visible bimodal distribution from master equation (well-mixed, black line) and (inhomogeneous) <i>Smoldyn</i> simulations for <i>D</i> = 3 (<i>X</i>) and 1 (<i>X</i>₂) (blue line) and <i>D</i> = 30 (<i>X</i>) and 10 (<i>X</i>₂) (red line) in units of <i>μm</i>²/<i>s</i>, the latter being typical protein diffusion constants in the cytoplasm. System was classified bistable when 10,000-long simulations (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0121681#sec010" target="_blank">Materials and Methods</a>) started in low and high states showed at least one reversible switch. Note that parameters are converted to physical units here (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0121681#sec010" target="_blank">Materials and Methods</a> for details). Hence, a 10,000-long-simulation corresponds to a duration of 2.78h, which is a very conservative estimate of cell-division times in bacteria and yeast. Shaded areas indicate bacterial (dark) and eukaryotic nuclear (light) volumes for comparison.