Figure 4

Performance of recruitment and combined spreading mechanisms with adjusted RE. The rows show data for the (A) modification induced recruitment mechanism, RE = 2, k _recruitment = 4.8 s^-1 and (B) combined diffusion and recruitment mechanism, RE = 0.1, k _recruitment = 0.24 s^-1. The other parameters used in these simulations are listed in Table 1. (A, B) In column i the stationary histone modification patterns as predicted by the model are shown. The y-axis indicates the probability per nucleosome to be modified or occupied by a methyltransferase (Mt). Red: methylation mark, orange: methyltransferase, green: acetylation mark, and black: unmodified state. In the second column (labeled ii), the time to establish a stationary state of methylation on the gene is displayed. Simulations started from a condition in which all the nucleosomes are in the A state. The dark orange error bars contain 50% of the data points around the median and the light orange error bars show the minimal and maximal value of the number of methylated nucleosomes (binned per second). An example trace of a single simulation is shown in black. In the third column (labeled iii), the probability distribution of the total transferase number and the total modification amount at steady state are displayed (same color coding as in column i). Column iv displays the relaxation dynamics. The error bars in column iv have the same meaning as in column ii. The simulations are initiated with all nucleosomes in the methylated state and occupied with methyltransferases, influx of new methyltransferase is not allowed at the initiation site.