CATABOLITE INACTIVATION OF FRUCTOSE-1,6-BISPHOSPHATASE OF SACCHAROMYCES-CEREVISIAE - DEGRADATION OCCURS VIA THE UBIQUITIN PATHWAY

Catabolite inactivation of fructose-1,6-bisphosphatase (EBPase), a key enzyme in gluconeogenesis, is due to phosphorylation and subsequent d egradation in the yeast Saccharomyces cerevisiae. The degradation proc ess of the enzyme had been shown to depend on the action of the protea some. Here we report that components of the ubiquitin pathway target F BPase to proteolysis. Upon glucose addition to yeast cells cultured on nonfermentable carbon sources FBPase is ubiquitinated in vivo. A mult iubiquitin chain containing isopeptide linkages at Lys(48) of ubiquiti n is attached to FBPase. Formation of a multiubiquitin chain is a prer equisite for the degradation of FBPase. Catabolite degradation of FBPa se is dependent on the ubiquitin-conjugating enzymes Ubc1, Ubc4, and U bc5. The 26 S proteasome is involved in the degradation process.