Ubiquitin-specific protease%3B situated in the base subcomplex of the 26S proteasome%2C releases free ubiquitin from branched polyubiquitin chains en bloc%2C rather than from the distal tip of the chain%3B negatively regulates degradation of ubiquitinated proteins by the proteasome%3B works in opposition to Hul5p polyubiquitin elongation activity%3B mutant has aneuploidy tolerance%3B human homolog UBP14 complements yeast null mutant
