PROTEIN TARGETING AND DEGRADATION IN THE YEAST VACUOLE

Protein degradation is an essential process in cells. Degradation of i ntracellular proteins increases when cells are starved of nutrients. L ysosomes are responsible for the enhanced protein degradation during s tarvation. To understand the degradation process that occurs in lysoso mes, we studied the catabolite inactivation of fructose-1,6-bisphospha tase (FBPase) in Saccharomyces cerevisiae. Fructose-1,6-bisphosphatase , a key enzyme in the gluconeogenesis pathway, is induced when cells a re starved of glucose and is degraded when cells are replenished with glucose. We have shown that catabolite inactivation of FBPase is media ted by a selective import of the enzyme into the vacuole (yeast lysoso me) for degradation. Glucose-induced degradation of FBPase serves to r egulate metabolism to prevent the energy futile cycle. In addition to FBPase, we have also demonstrated that peroxisomes, which are importan t in the oxidation of fatty acids, are delivered to the vacuole for de gradation in response to glucose. Furthermore, the galactose transport er, which is induced when cells are grown in galactose, is internalize d and delivered to the vacuole for degradation when cells are transfer red to glucose.