DNA Binding, Annealing, and Strand Exchange Activities of Brh2 Protein from Ustilago maydis

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• 作者：Nayef Mazloum ; Qingwen Zhou ; William K. Holloman
• 刊名：Biochemistry
• 出版年：2007
• 出版时间：June 19, 2007
• 年：2007
• 卷：46
• 期：24
• 页码：7163 - 7173
• 全文大小：438K
• 年卷期：v.46,no.24(June 19, 2007)
• ISSN：1520-4995

文摘

Brh2 is the Ustilago maydis ortholog of the BRCA2 tumor suppressor. It functions in repairof DNA by homologous recombination by controlling the action of Rad51. A critical aspect in the controlappears to be the recruitment of Rad51 to single-stranded DNA regions exposed as lesions after damageor following a disturbance in DNA synthesis. In previous experimentation, Brh2 was shown to nucleateformation of the Rad51 nucleoprotein filament that becomes the active element in promoting homologouspairing and DNA strand exchange. Nucleation was found to be initiated at junctions of double-strandedand single-stranded DNA. Here we investigated the DNA binding specificity of Brh2 in more detail usingoligonucleotide substrates. We observed that Brh2 prefers partially duplex structures with single-strandedbranches, flaps, or D-loops. We found also that Brh2 has an inherent ability to promote DNA annealingand strand exchange reactions on free as well as RPA-coated substrates. Unlike Rad51, Brh2 was able topromote DNA strand exchange when preincubated with double-stranded DNA. These findings raise thenotion that Brh2 may have roles in homologous recombination beyond the previously established Rad51mediator activity.