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J. Cell Biol.,
Volume 140, Number 6, March 23, 1998 1347-1356
Department of Cell Biology, Harvard Medical School, Boston, Massachussets 02115
Glucose regulates the degradation of the key
gluconeogenic enzyme, fructose-1,6-bisphosphatase
(FBPase), in Saccharomyces cerevisiae. FBPase is targeted from the cytosol to a novel type of vesicle, and
then to the vacuole for degradation when yeast cells are
transferred from medium containing poor carbon
sources to fresh glucose. To identify proteins involved
in the FBPase degradation pathway, we cloned our first
VID (vacuolar import and degradation) gene. The
VID24 gene was identified by complementation of the
FBPase degradation defect of the vid24-1 mutant.
Vid24p is a novel protein of 41 kD and is synthesized in
response to glucose. Vid24p is localized to the FBPase-containing vesicles as a peripheral membrane protein.
In the absence of functional Vid24p, FBPase accumulates in the vesicles and fails to move to the vacuole,
suggesting that Vid24p regulates FBPase targeting from the vesicles to the vacuole. FBPase sequestration
into the vesicles is not affected in the vid24-1 mutant,
indicating that Vid24p acts after FBPase sequestration
into the vesicles has occurred. Vid24p is the first protein identified that marks the FBPase-containing vesicles and plays a critical role in delivering FBPase from
the vesicles to the vacuole for degradation.
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