<p>The Blasi et al. (2016) [13] model selection problem in PEtab Select.</p>

<p><b>(a)</b> The reaction network for the published best model, represented as a graph similarly to <a href="ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1014774#pcbi.1014774.g002" target="_blank">Figs 2b</a>-<a href="ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1014774#pcbi.1014774.g002" target="_blank">2c</a>’. The histone chemical species can undergo acetylation reactions at four different positions (5, 8, 12, and 16).

Nodes are acetylation states (motifs) of the histone, and arrows are acetylation reactions. The model selection problem involves two different possibilities for the rate constant of each reaction; it is either: the shared basal rate constant (the value is fixed to 1), or an estimated motif-specific rate constant (the value is estimated). The model selection problem is to identify the reactions with motif-specific rate constants, and the published best model contains seven (solid arrows). <b>(b)</b> There are 32 reactions, and therefore 32 independent hypotheses for motif-specific rate constants.