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Publication Abstract from PubMed

The BRCA1-BARD1 tumour suppressor is an E3 ubiquitin ligase necessary for the repair of DNA double-strand breaks by homologous recombination(1-10). The BRCA1-BARD1 complex localizes to damaged chromatin after DNA replication and catalyses the ubiquitylation of histone H2A and other cellular targets(11-14). The molecular bases for the recruitment to double-strand breaks and target recognition of BRCA1-BARD1 remain unknown. Here we use cryo-electron microscopy to show that the ankyrin repeat and tandem BRCT domains in BARD1 adopt a compact fold and bind to nucleosomal histones, DNA and monoubiquitin attached to H2A amino-terminal K13 or K15, two signals known to be specific for double-strand breaks(15,16). We further show that RING domains(17) in BRCA1-BARD1 orient an E2 ubiquitin-conjugating enzyme atop the nucleosome in a dynamic conformation, primed for ubiquitin transfer to the flexible carboxy-terminal tails of H2A and variant H2AX. Our work reveals a regulatory crosstalk in which recognition of monoubiquitin by BRCA1-BARD1 at the N terminus of H2A blocks the formation of polyubiquitin chains and cooperatively promotes ubiquitylation at the C terminus of H2A. These findings elucidate the mechanisms of BRCA1-BARD1 chromatin recruitment and ubiquitylation specificity, highlight key functions of BARD1 in both processes and explain how BRCA1-BARD1 promotes homologous recombination by opposing the DNA repair protein 53BP1 in post-replicative chromatin(18-22). These data provide a structural framework to evaluate BARD1 variants and help to identify mutations that drive the development of cancer.

Mechanisms of BRCA1-BARD1 nucleosome recognition and ubiquitylation.,Hu Q, Botuyan MV, Zhao D, Cui G, Mer E, Mer G Nature. 2021 Aug;596(7872):438-443. doi: 10.1038/s41586-021-03716-8. Epub 2021 , Jul 28. PMID:34321665^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.