Has deubiquitinating activity towards 'Lys-48'- and 'Lys-63'-linked polyubiquitin chains. 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). Belongs to the DeSI family.