FIGURE 11:

Model of energy-dependent steps in adaptor recruitment. The steps illustrated may occur concurrently or in a different sequence than illustrated. Before energy input, Arf is localized to membranes, but Pik1 and adaptors are cytosolic. 1) On availability of GTP, Pik1 becomes localized and activated. 2) On availability of ATP, Pik1 synthesizes PI4p; however, this is not sufficient for adaptor recruitment. 3) Adaptors are recruited only when a third, uncharacterized factor has access to sufficient ATP. All three activities—Arf1, Pik1 and this third factor—are required for localization of adaptors to membranes during glucose starvation.