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bioRxiv · 10.1101/2020.06.01.127951

BARD1 links histone H2A Lysine-15 ubiquitination to initiation of BRCA1-dependent homologous recombination

Becker, J. R.·Bonnet, C.·Clifford, G.·Groth, A.·Wilson, M. D.·Chapman, J. R.
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Abstract

Protein ubiquitination at sites of DNA double-strand breaks (DSBs) by RNF168 recruits BRCA1 and 53BP1, mediators of the homologous recombination (HR) and non-homologous end joining (NHEJ) DSB repair pathways, respectively. While NHEJ relies on 53BP1 binding to ubiquitinated Lysine 15 on H2A-type histones (H2AK15ub), an RNF168-dependent modification, the mechanism linking RNF168 to BRCA1 recruitment during HR has remained unclear. Here, we identify a tandem BRCT domain ubiquitin-dependent recruitment motif (BUDR) in BARD1 - BRCA1s obligate partner protein - that binds H2AK15ub directly, thereby recruiting BRCA1 to DSBs. BARD1 BUDR mutations compromise HR, and render cells hypersensitive to PARP inhibition and cisplatin treatment. We find that BARD1-nucleosome interactions require BUDR binding to H2AK15ub and ankyrin repeat domain-mediated binding of the histone H4 tail, specifically when unmethylated on Lysine-20 (H4K20me0), a state limited to post replicative chromatin. Finally, we demonstrate that by integrating DNA damagedependent H2AK15ub and DNA replication-dependent H4K20me0 signals at sites of DNA damage, BARD1 coordinates BRCA1-dependent HR with 53BP1 pathway antagonization, establishing a simple paradigm for the governance of DSB repair pathway choice.

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Becker, J. R., Bonnet, C., Clifford, G., Groth, A., Wilson, M. D., Chapman, J. R.. 2020-06-01. BARD1 links histone H2A Lysine-15 ubiquitination to initiation of BRCA1-dependent homologous recombination. https://doi.org/10.1101/2020.06.01.127951

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