A Mathematical Model of the G1/S Transition for the Budding Yeast

A mathematical model of the G1/S transition is proposed, for the budding yeast Saccharomyces cerevisiae. It is known in biology that such a transition is promoted by multistep phosphorylation processes leading to the activation of the over 200 G1/S regulon genes. Feedback mechanisms play an active role, since part of the enzymes catalyzing the phosphorylation reactions are expressed by the G1/S regulon. The proposed Mathematical model is a Stochastic Hybrid System, since it merges such discrete features (modeled by means of Chemical Master Equations) with a continuous part related to protein and ribosome concentrations. The model manages to reproduce a large variety of available experimental data and suggests new experiments (carried out at the University of Milano Bicocca) that further validate the model by means of independent data. Results have been recently published on Nature Communications.