The Fab1 phosphatidylinositol kinase pathway in the regulation of vacuole morphology

Yeast vacuoles are very dynamic structures that must respond to changes in extracellular osmolarity by rapidly altering their size, thereby releasing or taking up water and ions. Further, the need to accommodate a constant biosynthetic influx of membrane and to partition vacuoles during cell division necessitates precise regulation of the size and shape of the vacuole. While it is has been shown that the lipid kinase Fab1p and its product phosphatidylinositol 3,5-bisphosphate, and not the mitogen-activated protein kinase Hog1p, are central to this regulatory pathway, key effectors still await identification. Atg18p is the most recently identified candidate for a Fab1p effector mediating the largely uncharacterized processes of vesicle fission and membrane recycling at the vacuole.