Figure 10.

Stt4p- or Pik1p-dependent phosphorylation of PtdIns leads to the production of distinct pools of PtdIns(4)P. Sac1p specifically turns over a pool of PtdIns(4)P pool generated by Stt4p, whereas Sjl proteins are potential candidate phosphatases for Pik1p-generated PtdIns(4)P turnover in the Golgi. The proposed roles for the different PtdIns(4)P pools are indicated. The Stt4p/Sac1p-dependent PtdIns(4)P pool is required for vacuole morphology, actin cytoskeleton organization, and regulation of neutral lipids storage, whereas the Pik1p-dependent PtdIns(4)P pool is essential for secretory vesicle formation from the Golgi and maintenance of Golgi/endosome morphology.