Deubiquitinating enzyme involved in DNA repair and reassembly of the Golgi apparatus and the endoplasmic reticulum following mitosis (PubMed:12473691, PubMed:15037600). Necessary for VCP-mediated reassembly of Golgi stacks after mitosis (PubMed:12473691, PubMed:15037600). Plays a role in VCP-mediated formation of transitional endoplasmic reticulum (tER) (PubMed:12473691, PubMed:15037600). Mediates dissociation of the ternary complex containing STX5A, NSFL1C and VCP (PubMed:12473691, PubMed:15037600). Also involved in DNA repair following phosphorylation by ATM or ATR: acts by catalyzing deubiquitination of SPRTN, thereby promoting SPRTN recruitment to chromatin and subsequent proteolytic cleavage of covalent DNA-protein cross-links (DPCs) (By similarity). Hydrolyzes 'Lys-11'- and 'Lys-48'-linked polyubiquitin chains (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). Binds VCP and the ternary complex containing STX5A, NSFL1C and VCP. Associated with Golgi stacks and endoplasmic reticulum (PubMed:12473691). Displays cytoplasmic to nuclear translocation in response to DNA-protein cross-links (DPCs)-inducing agents (By similarity). Widely expressed. Phosphorylated at Ser-1206 by ATM or ATR following induction of covalent DNA-protein cross-links (DPCs).