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). Found both cytoplasmic and nuclear in cytotrophoblasts and decidual cells. Expressed in the placenta at all stages of pregnancy. Expression increases as pregnancy progresses. 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.