Figure 2

Biochemically realistic model of the HOG pathway three-component phospho-relay in S. cerevisiae . A Cartoon diagram of the phospho-relay indicating the quaternary structure of each component and the four relevant phosphorylation sites. Phospho-transfer proceeds from Sln1 (after autophosphorylation on H576 and transfer to D1144) to Ypd1 to Ssk1, as indicated by the numbers in circles. B Crystal structure of Ypd1 (green) in complex with the response regulator domain of Sln1 (Sln1-R1, red). Drawn from data presented in [18]. C Reaction network diagram describing our model of the phospho-relay. The network includes nearly all possible interactions between the three proteins subject to the biochemical assumptions outlined in the main text. For clarity, the reaction network is color-coded to indicate the groups of reactions involved in each phosphorylation event. S denotes Sln1, Y denotes Ypd1, and K denotes Ssk1. Phosphorylated residues are denoted by p, unphosphorylated residues by o. D Directed graph describing the subnetwork involving phosphorylation and dephosphorylation of Ssk1. The graph contains four loops that are connected as a branched tree.