Required for the adaptation to the presence of glucose in the growth medium; mediates the degradation of enzymes involved in gluconeogenesis when cells are shifted to glucose-containing medium (PubMed:12686616). Required for proteasome-dependent catabolite degradation of fructose-1,6-bisphosphatase (FBP1) (PubMed:12686616). Accelerates proteasomal breakdown of ubiquitinated proteins as it disassembles free ubiquitin chains that would compete with ubiquitinated proteins to bind to the proteasome (PubMed:9305625). Thiol-dependent hydrolysis of ester, thioester, amide, peptide and isopeptide bonds formed by the C-terminal Gly of ubiquitin (a 76-residue protein attached to proteins as an intracellular targeting signal). Present with 3040 molecules/cell in log phase SD medium. Belongs to the peptidase C19 family.