Mechanisms of BRCA1-BARD1 nucleosome recognition and ubiquitylation

Nature. 2021 Aug;596(7872):438-443. doi: 10.1038/s41586-021-03716-8. Epub 2021 Jul 28.


The BRCA1-BARD1 tumour suppressor is an E3 ubiquitin ligase necessary for the repair of DNA double-strand breaks by homologous recombination1-10. The BRCA1-BARD1 complex localizes to damaged chromatin after DNA replication and catalyses the ubiquitylation of histone H2A and other cellular targets11-14. 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 breaks15,16. We further show that RING domains17 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 chromatin18-22. These data provide a structural framework to evaluate BARD1 variants and help to identify mutations that drive the development of cancer.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • BRCA1 Protein / metabolism*
  • Cryoelectron Microscopy
  • DNA Repair
  • Histones / chemistry
  • Histones / metabolism
  • Homologous Recombination
  • Humans
  • Models, Molecular
  • Mutation
  • Neoplasms / genetics
  • Nucleosomes / chemistry
  • Nucleosomes / genetics
  • Nucleosomes / metabolism*
  • Nucleosomes / ultrastructure
  • Protein Domains
  • Tumor Suppressor Proteins / chemistry
  • Tumor Suppressor Proteins / genetics
  • Tumor Suppressor Proteins / metabolism*
  • Tumor Suppressor Proteins / ultrastructure
  • Tumor Suppressor p53-Binding Protein 1 / antagonists & inhibitors
  • Tumor Suppressor p53-Binding Protein 1 / metabolism
  • Ubiquitin / metabolism*
  • Ubiquitin-Conjugating Enzymes / chemistry
  • Ubiquitin-Conjugating Enzymes / metabolism
  • Ubiquitin-Conjugating Enzymes / ultrastructure
  • Ubiquitin-Protein Ligases / chemistry
  • Ubiquitin-Protein Ligases / genetics
  • Ubiquitin-Protein Ligases / metabolism*
  • Ubiquitin-Protein Ligases / ultrastructure
  • Ubiquitination*


  • BRCA1 Protein
  • Histones
  • Nucleosomes
  • TP53BP1 protein, human
  • Tumor Suppressor Proteins
  • Tumor Suppressor p53-Binding Protein 1
  • Ubiquitin
  • UBE2D3 protein, human
  • Ubiquitin-Conjugating Enzymes
  • BARD1 protein, human
  • Ubiquitin-Protein Ligases