Uch2/Uch37 is the Major Deubiquitinating Enzyme Associated with the 26 S Proteasome in Fission Yeast

Conjugation of proteins to ubiquitin plays a central role for a number of cellular processes including endocytosis, DNA repair and degradation by the 26 S proteasome. However, ubiquitination is reversible as a number of deubiquitinating enzymes mediate the disassembly of ubiquitin–protein conjugates. Some deubiquitinating enzymes are associated with the 26 S proteasome contributing to and regulating the particleʹs activity. Here, we characterise fission yeast Uch2 and Ubp6, two proteasome associated deubiquitinating enzymes. The human orthologues of these enzymes are known as Uch37 and Usp14, respectively. We report that the subunit Uch2/Uch37 is the major deubiquitinating enzyme associated with the fission yeast 26 S proteasome. In contrast, the activity of Ubp6 appears to play a more regulatory and/or structural role involving the proteasome subunits Mts1/Rpn9, Mts2/Rpt2 and Mts3/Rpn12, as Ubp6 becomes essential when activity of these subunits is compromised by conditional mutations. Finally, when the genes encoding Uch2/Uch37 and Ubp6 are disrupted, the cells are viable without showing obvious signs of impaired ubiquitin-dependent proteolysis, indicating that other deubiquitinating enzymes may remedy for the redundancy of these enzymes.