Hydrolase that can remove conjugated ubiquitin from proteins and may therefore play an important regulatory role at the level of protein turnover by preventing degradation (By similarity). May be involved in TIV genomic DNA packaging in a manner related to the Gag polyproteins of the mammalian viruses. Thiol-dependent hydrolysis of ester, thioester, amide, peptide and isopeptide bonds formed by the C-terminal Gly of ubiquitin (a 76-residue protein attached to proteins as an intracellular targeting signal).