Ubiquitin-specific protease; removes ubiquitin and polyubiquitin from modified target proteins; controls K63 homeostasis during oxidative stress; deubiquitinates Rsp5p and is required for MVB sorting of membrane proteins; removes K63-linked polyubiquitin chains from Rps20p on free 40S ribosomal subunits for recycling to enhance ribosome-associated quality control (RQC) functionality