BRCA1-A and BRISC complex subunit BRE (also known as BRISC and BRCA1 A complex member 2; BRCC4; BRCC45) is a core component of both the BRCA1-A and BRISC complexes. BRCA1-A and BRISC are separate complexes with diverging function; they use the same core of subunits to perform very distinct biological tasks, and are found in all vertebrates. The BRCA1-A complex consists of BRE, Abraxas-1, BRCC36, MERIT40 and RAP80, and 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 double-strand breaks (DSB)s. This complex also possesses deubiquitinase (DUB) activity that specifically removes 'Lys-63'-linked ubiquitin on histones H2A and H2AX. In BRCA1-A, two heteropentamers, composed of BRCC36, ABRAXAS, BRE and MERIT40, form an arc-shaped complex; the two half-arcs contact each other through BRCC36 and its scaffold partner ABRAXAS. BRCC36 is connected to this arc via the ABRAXAS MPN domain. BRE forms the central bridge between the ABRAXAS-BRCC36 MPN domain dimer and MERIT40. BRE's N-terminal ubiquitin-conjugating enzyme variants domain (UEV-N) binds the ABRAXAS MPN, and BRE's C-terminal UEV domain (UEV-C) holds MERIT40 at the extremity of the arc. Loss of BRE significantly impairs BRCA1-A function, resulting in DNA repair defects and loss of cancer suppression. The BRISC complex consists of BRE, BRCC36, MERIT40 and Abraxas 2, and serves cellular stress response and immune signaling functions; it specifically cleaves 'Lys-63'-linked polyubiquitin, leaving the last ubiquitin chain attached to its substrates. The BRISC core has the same 2-fold symmetrical arc shape and is structurally similar to BRCA1-A; however, the conformation of BRE UEV-C and MERIT40 differs markedly. BRE has different functionality in the BRCA1-A and BRISC complexes: in BRCA1, it is involved in RAP80 integration, BRCA1 sequestration and ubiquitin binding, while in BRISC, it is involved in dimerization, SHMT2 recruitment, DUB inhibition and ubiquitin binding. A BRISC complex (containing of BRE/BRCC45, BRCC36, MERIT40, and Abraxas 2/KIAA0157) has been found in insects (Camponotus floridanus) and shown to efficiently degrade 'Lys-63'-linked chains. Homologs of genes encoding components of BRCA1-A and BRISC complexes have been found in plant genomes, including for BRE/BRCC45; plant homologs of BRCC36 have been shown to be involved in DNA repair; BRCC36-Abraxas 2 complexes have been found in Arabidopsis.
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