FIG. 3.

Multiple roles of the MAPKKK Ste11. The MAPKKK Ste11 can be activated by different signals resulting in different outputs. It can be activated by pheromones in the pheromone response pathway, resulting in mating (stippled arrows); a signal generated by nitrogen starvation in the pseudohyphal growth pathway, leading to morphological changes and growth properties of the cells (black arrows); and hyperosmolarity via Sho1 in the HOG pathway, resulting in the stress response (gray arrows). The mechanism by which activated Ste11 is prevented from inappropriately activating other pathways may involve scaffold proteins (see the text for details).