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Mol Cell. 2009 Jan 30;33(2):160-70. doi: 10.1016/j.molcel.2008.12.023.

Second-end capture in DNA double-strand break repair promoted by Brh2 protein of Ustilago maydis.

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Department of Microbiology and Immunology, Weill Cornell Medical College, New York, NY 10021, USA.


Brh2 plays a central role in the homologous recombination system of Ustilago maydis, mediating delivery of Rad51 to single-stranded DNA. Here we report that Brh2 can pair the displaced strand of a D loop with a complementary single-stranded DNA to form a duplexed, or double, D loop. The reaction emulates the second-end capture step envisioned in models of DNA double-strand break repair. This second-end capture reaction promoted by Brh2 proceeds efficiently when performed in the presence of Rad51 under conditions that block annealing by Rad52, or when the second single-stranded DNA substrate is replaced by double-stranded DNA. In a coupled reaction that requires extension of the D loop more than 200 nt by DNA synthesis in order to reveal a complementary region, Brh2 was also able to promote second-end capture and thus model a synthesis-dependent strand-annealing mechanism.

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