FIGURE 3 

Ultrasensitivity and bistable expression in response to TF stimulation. The steps in Figure 2 were iterated for systems with various numbers of nucleosomes N, feedback-to-noise ratios F=(1- ), and different levels of recruited HAT activity . The system was biased towards methylation by setting =2/3 (see Figure 2). The upper panels show the average fraction of acetylated nucleosomes A versus . The lower panels show the probabilities (lighter colours for higher) for the system to exist with a particular fraction of A nucleosomes A for the cases where F=5. The h values were obtained by fitting the curves to A- A₀^h/(k+^h), varying A₀, K and h.