Deubiquitinating enzyme (DUB) that controls levels of cellular ubiquitin through processing of ubiquitin precursors and ubiquitinated proteins. Thiol protease that recognizes and hydrolyzes a peptide bond at the C-terminal glycine of either ubiquitin or RUB1. Preferentially cleaves ubiquitin from peptides and small adducts. 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). Optimum pH is 8.5. Inactive at a pH below 6.5. Optimum temperature is 27 degrees Celsius. Can hydrolyze human UBB(+1), a mutated form of ubiquitin which is not effectively degraded by the proteasome and is associated with neurogenerative disorders. It can do so despite of the fact that the C-terminal 'Gly-76' of ubiquitin has been substituted for a tyrosine in UBB(+1). Belongs to the peptidase C12 family.