Figure 2.

Model for fungal Ras1 activation by Turgor. In the step labeled 1, glucose-binding by a G-protein coupled receptor leads to an increase in the GTP-bound Ras1 concentration at the lipid raft boundary mediated by a guanine exchange factor (GEF) such as Cdc25. In step 2, increased turgor exerts a membrane thinning effect that induces lateral transfer and clustering of GTP-bound Ras1 monomers out of lipid raft boundaries driven by a more favorable entropic environment. A similar lateral membrane transfer mechanism induced by cell swelling is proposed for H-Ras (see text).