Upon starving Saccharomyces cerevisiae of glucose, the key gluconeogenic enzymes fructose-1,6-bisphosphatase (FBPase), malate dehydrogenase (MDH2), isocitrate lyase (Icl1p) and phosphoenolpyruvate carboxykinase (Pck1p) are induced. When glucose is added to cells that have been starved for 3 days, these gluconeogenic enzymes are degraded in the vacuole via the vacuole import and degradation (Vid) pathway. Moreover, it has been determined that during glucose starvation, these cargo proteins interact with the target of rapamycin complex 1 (TORC1), which is comprised of Tor1p, Tco89p, Lst8p and Kog1p. However, following glucose replenishment, Tor1p dissociates from the cargo proteins. We have determined that cells overexpressing TOR1 inhibited the phosphorylation of FBPase and its subsequent degradation in the vacuole. Interestingly, while the deletion of TCO89 inhibited FBPase degradation, it did not inhibit the phosphorylation of FBPase. Both Tor1p and Tco89p were found in endosomes originating from the plasma membrane as well as in retrograde vesicles forming from the vacuole membrane. Here we further discuss our findings and elaborate on our current model of the Vid pathway.

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Journal Article

Authors

Alibhoy AA, Chiang HL

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