Genome stability relies on a network of interacting systems that detect and repair disturbances in the integrity of DNA. A central pathway that processes single-stranded DNA gaps and potentially lethal double-strand breaks in DNA that can occur during DNA replication employs a mechanism that repairs these lesions by homologous recombination. Primary components of this pathway in eukaryotes include Rad51 whose function is to search for DNA sequence homology and promote strand exchange, plus factors that enable, enhance, and control Rad51's activity. Among this constellation of Rad51-interacting proteins the master regulator is BRCA2, the product of a breast cancer susceptibility gene. BRCA2 in turn, is completely dependent upon its key interacting partner, Dss1, for activity. Through the concerted workings of this hierarchical complex comprised of Dss1, BRCA2, and Rad51, the homologous recombination system is harnessed to maintain stability and preserve the integrity of the genome. We seek to understand how BRCA2 function is regulated by Dss1 and to understand the role of BRCA2 in governing the activity of Rad51. We use the microbe Ustilago maydis as a model system for experimentation because it has a well-conserved BRCA2-homolog, Brh2, and is amenable to molecular genetic manipulations and analysis. The powerful attributes of this system open the way for gaining insight into BRCA2's molecular mechanism through avenues not immediately approachable in the vertebrate systems. Our primary objectives are to investigate the role of Dss1 as a regulator of Brh2, to examine how Brh2 controls the activity of Rad51, and to investigate how select proteins interact genetically with Brh2 and Rad51 to regulate homologous recombination activity. Our long-term goal is to provide knowledge of the function of BRCA2 and gain insight into how its dysfunction can lead to initiation of tumorigenic transformation.

Public Health Relevance

Initiating the progression to tumorigenesis can be provoked when the cellular systems responsible for maintaining genome stability are compromised. Repairing damaged DNA by homologous recombination comprises one of these system dedicated to preserving genomic integrity. An important gene that regulates homologous recombination encodes the BRCA2 protein, mutations in which cause early-onset breast cancer. This is a proposal to learn about the fundamental action of how BRCA2 works in regulating homologous recombination by studying a model microbial system.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
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Radiation Therapeutics and Biology Study Section (RTB)
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Janes, Daniel E
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Weill Medical College of Cornell University
Schools of Medicine
New York
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Zhou, Qingwen; Holloman, William K (2014) Dual DNA-binding domains shape the interaction of Brh2 with DNA. DNA Repair (Amst) 22:104-11
Yu, Eun Young; Kojic, Milorad; Holloman, William K et al. (2013) Brh2 and Rad51 promote telomere maintenance in Ustilago maydis, a new model system of DNA repair proteins at telomeres. DNA Repair (Amst) 12:472-9
Kojic, Milorad; Holloman, William K (2012) Brh2 domain function distinguished by differential cellular responses to DNA damage and replication stress. Mol Microbiol 83:351-61
Holloman, William K (2011) Unraveling the mechanism of BRCA2 in homologous recombination. Nat Struct Mol Biol 18:748-54
de Sena-Tomas, Carmen; Fernandez-Alvarez, Alfonso; Holloman, William K et al. (2011) The DNA damage response signaling cascade regulates proliferation of the phytopathogenic fungus Ustilago maydis in planta. Plant Cell 23:1654-65
Kojic, Milorad; Zhou, Qingwen; Fan, Jie et al. (2011) Mutational analysis of Brh2 reveals requirements for compensating mediator functions. Mol Microbiol 79:180-91
Zhou, Qingwen; Kojic, Milorad; Holloman, William K (2009) DNA-binding Domain within the Brh2 N Terminus Is the Primary Interaction Site for Association with DNA. J Biol Chem 284:8265-73
Mazloum, Nayef; Holloman, William K (2009) Second-end capture in DNA double-strand break repair promoted by Brh2 protein of Ustilago maydis. Mol Cell 33:160-70
Mazloum, Nayef; Holloman, William K (2009) Brh2 promotes a template-switching reaction enabling recombinational bypass of lesions during DNA synthesis. Mol Cell 36:620-30
Zhou, Qingwen; Mazloum, Nayef; Mao, Ninghui et al. (2009) Dss1 regulates interaction of Brh2 with DNA. Biochemistry 48:11929-38

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