Deubiquitinating enzyme that plays a key role in chromatin by mediating deubiquitination of histone H2A. Catalytic component of the PR-DUB complex, a complex that specifically mediates deubiquitination of histone H2A monoubiquitinated at 'Lys-119' (H2AK119ub1) (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). Component of the PR-DUB complex. Mainly nuclear. Binds to chromatin. Belongs to the peptidase C12 family. BAP1 subfamily.