title: Brh2 promotes a template-switching reaction enabling recombinational bypass of lesions during DNA synthesis.
abstract: Accumulating evidence for Rad51-catalyzed DNA strand invasion during double-strand break repair features a 3' single-stranded tail as the preferred substrate for reaction, but paradoxically, the preferred substrate in model reactions in vitro is the 5' end. Here, we examined the Rad51-promoted 5' end invasion reaction in the presence of Brh2, the BRCA2 family protein in Ustilago maydis. Using plasmid DNA and a homologous duplex oligonucleotide with 5' protruding single-stranded tail as substrates, we found that Brh2 can stimulate Rad51 to promote the formation of a four-stranded complement-stabilized D loop. In this structure, the incoming recessed complementary strand of the oligonucleotide has switched partners and can now prime DNA synthesis using the recipient plasmid DNA as template, circumventing a lesion that blocks elongation when the 5' protruding tail serves as template for fill-in synthesis. We propose that template switching promoted by Brh2 provides a mechanism for recombination-mediated bypass of lesions blocking synthesis during DNA replication.
authors: Department of Microbiology and Immunology, Weill Cornell Medical College, New York, NY 10065, USA.
authors: Nayef
authors: N
authors: Mazloum
authors: William K
authors: WK
authors: Holloman
mesh_terms: D004249:DNA Damage; D004261:DNA Replication; D004271:DNA, Fungal / Q000096:biosynthesis* / Q000737:chemistry; D005656:Fungal Proteins / Q000378:metabolism*; D009690:Nucleic Acid Conformation; D051135:Rad51 Recombinase / Q000378:metabolism; D011995:Recombination, Genetic; D013698:Templates, Genetic; D014588:Ustilago / Q000235:genetics*
chemical_list: D004271:DNA, Fungal; D005656:Fungal Proteins; D051135:Rad51 Recombinase