title: DNA binding, annealing, and strand exchange activities of Brh2 protein from Ustilago maydis.
abstract: Brh2 is the Ustilago maydis ortholog of the BRCA2 tumor suppressor. It functions in repair of DNA by homologous recombination by controlling the action of Rad51. A critical aspect in the control appears to be the recruitment of Rad51 to single-stranded DNA regions exposed as lesions after damage or following a disturbance in DNA synthesis. In previous experimentation, Brh2 was shown to nucleate formation of the Rad51 nucleoprotein filament that becomes the active element in promoting homologous pairing and DNA strand exchange. Nucleation was found to be initiated at junctions of double-stranded and single-stranded DNA. Here we investigated the DNA binding specificity of Brh2 in more detail using oligonucleotide substrates. We observed that Brh2 prefers partially duplex structures with single-stranded branches, flaps, or D-loops. We found also that Brh2 has an inherent ability to promote DNA annealing and strand exchange reactions on free as well as RPA-coated substrates. Unlike Rad51, Brh2 was able to promote DNA strand exchange when preincubated with double-stranded DNA. These findings raise the notion that Brh2 may have roles in homologous recombination beyond the previously established Rad51 mediator activity.
authors.affiliation: Department of Microbiology and Immunology, Cornell University Weill Medical College, New York, New York 10021, USA.
authors.forename: Nayef
authors.initials: N
authors.lastname: Mazloum
authors.forename: Qingwen
authors.initials: Q
authors.lastname: Zhou
authors.forename: William K
authors.initials: WK
authors.lastname: Holloman
mesh_terms: D051017:Apoptosis Regulatory Proteins; D024682:BRCA2 Protein / Q000378:metabolism; D001483:Base Sequence; D004247:DNA / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D051135:Rad51 Recombinase / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D051716:Replication Protein A / Q000235:genetics / Q000378:metabolism; D014588:Ustilago / Q000235:genetics / Q000378:metabolism*
chemical_list: D051017:Apoptosis Regulatory Proteins; C118024:BLID protein, human; D024682:BRCA2 Protein; C551750:BRCA2 protein, human; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D011994:Recombinant Proteins; D051716:Replication Protein A; D004247:DNA; D051135:Rad51 Recombinase