Ubiquitin thioesterase that acts at the late endosome/prevacuolar compartment to recover ubiquitin from ubiquitinated membrane proteins en route to the vacuole. Removes also ubiquitin from soluble proteins targeted to proteasomes. Is essential to maintain a normal level of free ubiquitin. Involved in the ammonium-induced down-regulation of the GAP1 permease and the UME3 destruction in response to oxidative stress. Has a role in the RAD9 checkpoint response to TOP1 poisons. Required for promoting coordination of DNA replication and avoids DNA overreplication.
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