SUPPLEMENTAL MATERIAL Positive Feedback Is Sufficient to Trigger Spontaneous Spatial Localization of Signaling Systems in Cells

General description of the model. We consider the diffusion of N particles in a cell, consisting of the cytosol, and the membrane. We assume the cell is a sphere of radius R. There are four different kinds of events which change the configuration of particles in the cell. • Spontaneous membrane association. A particle in the cytosol will move to a random location on the membrane at a rate of kon ([min −1]). • Spontaneous membrane disassociation. A particle on the membrane can move back to the cytosol. This happens with rate koff ([min −1]). • Membrane association through recruitment. A particle on the membrane can recruit a particle in the cytosol. The rate at which one particle recruits from the cytosol is proportional to the fraction of particles which are still in the cytosol. The proportionality constant is kfb ([min −1]). • Diffusion on membrane. Each particle on the membrane undergoes a Brownian motion with diffusion coefficient D ([μm2min−1]).