Metalloprotease that specifically cleaves \'Lys-63\'-linked polyubiquitin chains. Does not have activity toward \'Lys-48\'-linked polyubiquitin chains. Component of the BRCA1-A complex, a complex that specifically recognizes \'Lys-63\'-linked ubiquitinated histones H2A and H2AX at DNA lesions sites, leading to target the BRCA1-BARD1 heterodimer to sites of DNA damage at double-strand breaks (DSBs). In the BRCA1-A complex, it specifically removes \'Lys-63\'-linked ubiquitin on histones H2A and H2AX, antagonizing the RNF8-dependent ubiquitination at double-strand breaks (DSBs). Catalytic subunit of the BRISC complex, a multiprotein complex that specifically cleaves \'Lys-63\'-linked ubiquitin in various substrates. Mediates the specific \'Lys-63\'-specific deubiquitination associated with the COP9 signalosome complex (CSN), via the interaction of the BRISC complex with the CSN complex.