Involved in DNA damage response and double-strand break (DSB) repair. Component of the BRCA1-A complex, acting as a central scaffold protein that assembles the various components of the complex and mediates the recruitment of brca1. The BRCA1-A complex specifically recognizes 'Lys-63'-linked ubiquitinated histones H2A and H2AX at DNA lesion sites, leading to target the brca1-bard1 heterodimer to sites of DNA damage at DSBs. This complex also possesses deubiquitinase activity that specifically removes 'Lys-63'-linked ubiquitin on histones H2A and H2AX (By similarity). Component of the BRCA1-A complex. Component of the BRISC complex. Interacts directly (when phosphorylated at Ser-405) with brca1. Homodimer. The phosphorylated homodimer can interact directly with two brca1 chains, giving rise to a heterotetramer (By similarity). Localizes at sites of DNA damage at double-strand breaks (DSBs). Phosphorylation of Ser-405 of the pSXXF motif by ATM or ATR constitutes a specific recognition motif for the BRCT domain of BRCA1. Belongs to the FAM175 family. Abraxas subfamily.