Deubiquitinating enzyme involved in DNA repair and reassembly of the Golgi apparatus and the endoplasmic reticulum following mitosis (PubMed:32649882). Necessary for VCP-mediated reassembly of Golgi stacks after mitosis (By similarity). Plays a role in VCP-mediated formation of transitional endoplasmic reticulum (tER) (By similarity). Mediates dissociation of the ternary complex containing STX5A, NSFL1C and VCP (By similarity). 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) (PubMed:32649882). Hydrolyzes 'Lys-11'- and 'Lys-48'-linked polyubiquitin chains (PubMed:23827681). (Microbial infection) Regulates the duration of C.botulinum neurotoxin type A (BoNT/A) intoxication by catalyzing deubiquitination of Botulinum neurotoxin A light chain (LC), thereby preventing LC degradation by the proteasome, and accelerating botulinum neurotoxin intoxication in patients. 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 (By similarity). Displays cytoplasmic to nuclear translocation in response to DNA-protein cross-links (DPCs)-inducing agents (PubMed:32649882). Phosphorylated at Ser-1207 by ATM or ATR following induction of covalent DNA-protein cross-links (DPCs).