Double-stranded DNA binding function of RAD51 in DNA protection and its regulation by BRCA2

RAD51 and the breast cancer suppressor BRCA2 have critical functions in DNA double-strand (dsDNA) break repair by homologous recombination and the protection of newly replicated DNA from nucleolytic degrada-tion. The recombination function of RAD51 requires its binding to single-stranded DNA (ssDNA), whereas binding to dsDNA is inhibitory. Using reconstituted MRE11-, EXO1-, and DNA2-dependent nuclease reac-tions, we show that the protective function of RAD51 unexpectedly depends on its binding to dsDNA. The BRC4 repeat of BRCA2 abrogates RAD51 binding to dsDNA and accordingly impairs the function of RAD51 in protection. The BRCA2 C-terminal RAD51-binding segment (TR2) acts in a dominant manner to overcome the effect of BRC4. Mechanistically, TR2 stabilizes RAD51 binding to dsDNA, even in the presence of BRC4, promoting DNA protection. Our data suggest that RAD51???s dsDNA-binding capacity may have evolved together with its function in replication fork protection and provide a mechanistic basis for the DNA-protection function of BRCA2.

Automated summary

RAD51 and BRCA2 play critical roles in DNA repair and protection. RAD51 binds to single-stranded DNA for its recombination function, but binding to double-stranded DNA is inhibitory. Surprisingly, we found that the protective function of RAD51 actually depends on its binding to double-stranded DNA. The BRC4 repeat of BRCA2 disrupts RAD51 binding to double-stranded DNA and impairs its protective function. However, the C-terminal RAD51-binding segment (TR2) of BRCA2 overcomes the inhibitory effect of BRC4 and stabilizes RAD51 binding to double-stranded DNA, promoting DNA protection.