title: Activation of the E3 ligase function of the BRCA1/BARD1 complex by polyubiquitin chains.
abstract: Loss of the tumour suppressor BRCA1 results in profound chromosomal instability. The fundamental defect underlying this catastrophic phenotype is not yet known. In vivo, BRCA1 forms a heterodimeric complex with BARD1. Both proteins contain an N-terminal zinc RING-finger domain which confers E3 ubiquitin ligase activity. We have isolated full-length human BRCA1/BARD1 complex and have shown that it has a dual E3 ubiquitin ligase activity. First, it mediates the monoubiquitylation of nucleosome core histones in vitro, including the variant histone H2AX that co-localizes with BRCA1 at sites of DNA damage. Secondly, BRCA1/BARD1 catalyses the formation of multiple polyubiquitin chains on itself. Remarkably, this auto-polyubiquitylation potentiates the E3 ubiquitin ligase activity of the BRCA1/BARD1 complex >20-fold. Even though BRCA1 has been reported to associate with a C-terminal ubiquitin hydrolase, BAP1, this enzyme does not appear to function in the deubiquitylation of the BRCA1/BARD1 complex.
authors.affiliation: MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK.
authors.forename: Donna L
authors.initials: DL
authors.lastname: Mallery
authors.forename: Cassandra J
authors.initials: CJ
authors.lastname: Vandenberg
authors.forename: Kevin
authors.initials: K
authors.lastname: Hiom
mesh_terms: D019313:BRCA1 Protein / Q000737:chemistry* / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism; D002384:Catalysis; D004249:DNA Damage; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D005822:Genetic Vectors; D006657:Histones / Q000378:metabolism; D006801:Humans; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000378:metabolism; D013379:Substrate Specificity; D025521:Tumor Suppressor Proteins; D025801:Ubiquitin / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D016335:Zinc Fingers
chemical_list: D019313:BRCA1 Protein; D002352:Carrier Proteins; D006657:Histones; D011994:Recombinant Proteins; D025521:Tumor Suppressor Proteins; D025801:Ubiquitin; C102449:BARD1 protein, human; D044767:Ubiquitin-Protein Ligases