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. Component of the ARISC complex, at least composed of UIMC1/RAP80, ABRAXAS1, BRCC3/BRCC36, BABAM2 and BABAM1/NBA1. Component of the BRCA1-A complex, at least composed of the BRCA1, BARD1, UIMC1/RAP80, ABRAXAS1, BRCC3/BRCC36, BABAM2 and BABAM1/NBA1. In the complex, interacts directly with UIMC1/RAP80, BRCC3/BRCC36 and BABAM2. Homodimer. Interacts directly (when phosphorylated at Ser-407) with BRCA1. The phosphorylated homodimer can interact directly with two BRCA1 chains, giving rise to a heterotetramer. Binds polyubiquitin. Localizes at sites of DNA damage at double-strand breaks (DSBs). Phosphorylation of Ser-407 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.