FIG 7.

Model for Ump2 interaction with Rho1 signaling. Previous work provided evidence for the role of Rho1 in negatively affecting Rac1 and thereby blocking filamentation (26). Conditions of ammonium limitation are sensed by Ump2, which relays the signal to downstream effectors to help decide the fate of the cells under such nutrient limiting conditions. Under such conditions, when Ump2 is expressed, it interacts with Rho1 and sequesters it away from its competition with Rac1, thereby allowing/causing filamentation. Specifically, since Cdc24 is the GEF for both Rho1 and Rac1, the model posits that Ump2 sequestration of Rho1 allows Cdc24 to activate Rac1 preferentially under conditions of ammonium limitation.