Ub-specific protease; Ubp3p-Bre5p complex subunit that mediates retention of Golgi membrane proteins; deubiquitinates Sec23p and Sec27p with Bre5p, regulating Golgi-ER retrograde transport; cleaves K48-linked di-Ub and K48/K63 mixed-linkage polyUb chains from Rps20p on translating ribosomes to enhance RQC; phosphorylated by Hog1p to regulate the osmotic stress response; inhibits Ras/PKA signaling through Ira2p; role in ribophagy; protein abundance increases in response to DNA replication stress