Background: MERIT40 (mediator of RAP80 interactions and targeting subunit of 40 kDa) is a component of the BRCA1-A complex, a complex that specifically recognizes 'Lys-63'-linked ubiquitinated histones H2A and H2AX at DNA lesions sites and leads to targeting of the BRCA1-BARD1 heterodimer to sites of DNA damage at double-strand breaks (DSBs). In the BRCA1-A complex, it is required for the complex integrity and its localization at DSBs. MERIT40 probably also plays a role as a component of the BRISC complex, a multiprotein complex that specifically cleaves 'Lys-63'-linked ubiquitin [taken from the Universal Protein Resource (UniProt) Q9NWV8].