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The BRCA2 homologue Brh2 nucleates RAD51 filament formation at a dsDNA–ssDNA junction

Abstract

The BRCA2 tumour suppressor1 is essential for the error-free repair of double-strand breaks (DSBs) in DNA by homologous recombination2,3. This is mediated by RAD51, which forms a nucleoprotein filament with the 3′ overhanging single-stranded DNA (ssDNA) of the resected DSB, searches for a homologous donor sequence, and catalyses strand exchange with the donor DNA4. The 3,418-amino-acid BRCA2 contains eight 30-amino-acid BRC repeats that bind RAD51 (refs 5, 6) and a 700-amino-acid DBD domain that binds ssDNA7. The isolated BRC and DBD domains have the opposing effects of inhibiting8,9 and stimulating recombination7, respectively, and the role of BRCA2 in repair has been unclear. Here we show that a full-length BRCA2 homologue (Brh2) stimulates Rad51-mediated recombination at substoichiometric concentrations relative to Rad51. Brh2 recruits Rad51 to DNA and facilitates the nucleation of the filament, which is then elongated by the pool of free Rad51. Brh2 acts preferentially at a junction between double-stranded DNA (dsDNA) and ssDNA, with strict specificity for the 3′ overhang polarity of a resected DSB. These results establish a BRCA2 function in RAD51-mediated DSB repair and explain the loss of this repair capacity in BRCA2-associated cancers.

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Figure 1: Substoichiometric amounts of Brh2–Dss1 stimulate Rad51-mediated strand exchange.
Figure 2: Brh2 facilitates filament nucleation by displacing RPA.
Figure 3: Strand exchange yields by substoichiometric Rad51 decrease with increasing junction-readout sequence distance.

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Acknowledgements

We thank H. Erdument-Bromage of the Sloan-Kettering Microchemistry Facility and D. King from the HHMI mass spectrometry laboratory at U.C. Berkeley for N-terminal sequence and mass spectroscopic analysis; and P. D. Jeffrey and members of the Pavletich laboratory for helpful discussions. This work was supported by the NIH, the Howard Hughes Medical Institute, and the Arthur and Rochelle Belfer Foundation.

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Correspondence to Nikola P. Pavletich.

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This file contains eight Supplementary Figures, their legends, description of Methods and further references. (DOC 3913 kb)

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Yang, H., Li, Q., Fan, J. et al. The BRCA2 homologue Brh2 nucleates RAD51 filament formation at a dsDNA–ssDNA junction. Nature 433, 653–657 (2005). https://doi.org/10.1038/nature03234

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