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 (PubMed:24075985). Component of the BRCA1-A complex, at least composed of BRCA1, BARD1, UIMC1/RAP80, ABRAXAS1, BRCC3/BRCC36, BABAM2 and BABAM1/NBA1. In the complex, interacts directly with UIMC1/RAP80, BRCC3/BRCC36 and BABAM2. Interacts directly (when phosphorylated at Ser-406) with BRCA1. Homodimer. The homodimer interacts directly (when phosphorylated at Ser-404 and Ser-406) 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-406 of the pSXXF motif by ATM or ATR constitutes a specific recognition motif for the BRCT domain of BRCA1 (PubMed:17643121, PubMed:17525340, PubMed:17643122). Ionizing radiation promotes rapid phosphorylation at Ser-404 and Ser-406 by ATM; this promotes recruitment of BRCA1 to sites of DNA damage (PubMed:26778126). Disease susceptibility is associated with variants affecting the gene represented in this entry. Belongs to the FAM175 family. Abraxas subfamily. Truncated N-terminus.