Abstract
Catabolite inactivation of fructose-1,6-bisphosphatase (FBPase), a key enzyme in gluconeogenesis, is due to phosphorylation and subsequent degradation in the yeast Saccharomyces cerevisiae. The degradation process of the enzyme had been shown to depend on the action of the proteasome. Here we report that components of the ubiquitin pathway target FBPase to proteolysis. Upon glucose addition to yeast cells cultured on nonfermentable carbon sources FBPase is ubiquitinated in vivo. A multiubiquitin chain containing isopeptide linkages at Lys48 of ubiquitin is attached to FBPase. Formation of a multiubiquitin chain is a prerequisite for the degradation of FBPase. Catabolite degradation of FBPase is dependent on the ubiquitin-conjugating enzymes Ubc1, Ubc4, and Ubc5. The 26 S proteasome is involved in the degradation process.
Highlights
Specific and rapid degradation of certain proteins is a fundamental mechanism in many biological processes, including embryonic development, cell proliferation, cell cycle control, and metabolic regulation [1]
Addition of glucose to yeast cells grown on a nonfermentable carbon source causes a rapid inactivation of FBPase due to phosphorylation and subsequent degradation [3,4,5]
When pulse-labeled FBPase was immunoprecipitated during catabolite inactivation in cells expressing wild-type ubiquitin from a 2-m plasmid, at least two additional labeled species with higher mass than FBPase could be detected in the precipitates (Fig. 1A, lanes 2 and 3)
Summary
Specific and rapid degradation of certain proteins is a fundamental mechanism in many biological processes, including embryonic development, cell proliferation, cell cycle control, and metabolic regulation [1]. Catabolite degradation of FBPase is dependent on the ubiquitin-conjugating enzymes Ubc1, Ubc4, and Ubc5. When pulse-labeled FBPase was immunoprecipitated during catabolite inactivation in cells expressing wild-type ubiquitin from a 2-m plasmid, at least two additional labeled species with higher mass than FBPase could be detected in the precipitates (Fig. 1A, lanes 2 and 3).
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