In Vitro Reconstitution of Glucose-induced Targeting of Fructose-1, 6-bisphosphatase into the Vacuole in Semi-intact Yeast Cells

Fructose-1,6-bisphosphatase (FBPase), the key enzyme in gluconeogenesis in the yeast Saccharomyces cerevisiae, is induced when cells are grown in medium containing poor carbon sources. FBPase is targeted from the cytosol to the vacuole for degradation when glucose-starved yeast cells are replenished with fresh glucose. In this study, we report the reconstitution of the glucose-induced import of FBPase into the vacuole in semi-intact yeast cells using radiolabeled FBPase, an ATP regenerating system and cytosol. The import of FBPase was defined as the fraction of the FBPase that was sequestered inside a membrane-sealed compartment. FBPase import requires ATP hydrolysis and is stimulated by cytosolic proteins. Furthermore, the import of FBPase is a saturable process. FBPase import is low in the glucose-starved cells and is stimulated in the glucose-replenished cells. FBPase accumulates to a higher level in the pep4 cell, suggesting that FBPase is targeted to the vacuole for degradation. Indirect immunofluorescence microscopy studies demonstrate that the imported FBPase is localized to the vacuole in the permeabilized cells. Thus, the glucose-induced targeting of FBPase into the vacuole can be reproduced in our in vitro system.