Ubiquitin-protein hydrolase involved both in the processing of ubiquitin precursors and of ubiquitinated proteins. This enzyme is a thiol protease that recognizes and hydrolyzes a peptide bond at the C-terminal glycine of ubiquitin (By similarity). Also binds to free monoubiquitin and may prevent its degradation in lysosomes (By similarity). The homodimer may have ATP-independent ubiquitin ligase activity (By similarity). 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). Monomer. Homodimer. Interacts with COPS5 and SNCA (By similarity). Neurons and cells of the diffuse neuroendocrine system and their tumors. O-glycosylated. In contrast to UCHL3, does not hydrolyze a peptide bond at the C-terminal glycine of NEDD8. Belongs to the peptidase C12 family. The homodimer may have ATP-independent ubiquitin ligase activity. However, in another study, UCHL1 was shown to lack ubiquitin ligase activity.