Model parameter 1.

1Unit conversions are based on a cell cytoplasmic volume of L [59].2For each binding reaction, the association rate constant () is assumed to be .3The half-life of phosphorylation is approximately 10 min [74].4The selected parameter values allow the model to reproduce a number of experimental observations, including 1) the steady-state level, 2) the half-lives of and S33/S37-mutated (Fig. S1), and 3) the kinetics of dephosphorylation of at S33/S37 and S45 upon treatment with LiCl (Fig. S2).See Materials and Methods for more details.