4 Biogenesis and Function of the Yeast Vacuole

Abstract

I. INTRODUCTION
A defining characteristic of all eukaryotic cells is the presence of distinct endomembrane organelles. These compartments allow a cell to carry out competing processes in separate environments suited to the particular requirements of each process (e.g., biosynthesis vs. degradation). The presence of endomembrane organelles requires not only the formation and maintenance of the lipid components that delineate the different compartments, but also the synthesis and targeting of proteins that serve either structural or enzymatic functions in the organelles. The vacuole of Saccharomyces cerevisiae is a large organelle, comprising as much as 25% of the cellular volume (Wiemken and Durr 1974). There are some indications that vacuolar morphology is correlated with the cell’s position in the cell cycle (Hartwell 1970; Wiemken et al. 1970; Jones et al. 1993); logarithmically growing cells often have a multilobed vacuole, with interconnections between lobes indicative of a reticulum, whereas stationary-phase cells and cells in G₁ typically have a single large vacuole that is relatively less dense (Hartwell 1970; Wiemken et al. 1970; Preston et al. 1989; Pringle et al. 1989; Jones et al. 1993). The vacuole is a very dynamic organelle. When cells are starved of a carbon source, the vacuolar lobes rapidly fuse to give a single large vacuole that is less dense than prior to fusion; it will be phase bright, whereas the reticular vacuole is not. Refeeding results in a rapid return to the denser reticular form (Pringle et al. 1989).

The yeast vacuole shares features with lysosomes. It contains...