The switch from gluconeogenesis to glycolysis in yeast has been shown to require ubiquitin-proteasome dependent elimination of the key enzyme fructose-1,6-bisphosphatase (FBPase). Prior to proteasomal degradation, polyubiquitination of the enzyme occurs via the ubiquitin-conjugating enzymes Ubc1, Ubc4, Ubc5 and Ubc8 in conjunction with a novel multi-subunit ubiquitin ligase, the Gid complex. As an additional machinery required for the catabolite degradation process, we identified the trimeric Cdc48(Ufd1-Np14) complex and the ubiquitin receptors Dsk2 and Rad23. We show that this machinery acts between polyubiquitination of FBPase and its degradation by the proteasome. (C) 2010 Elsevier Inc. All rights reserved.