Article

The Rad51 paralog complexes BCDX2 and CX3 act at different stages in the BRCA1-BRCA2 dependent homologous recombination pathway.

Molecular Biology Program and Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, 10021, USA.
Molecular and Cellular Biology (Impact Factor: 5.04). 11/2012; 33(2). DOI: 10.1128/MCB.00465-12
Source: PubMed

ABSTRACT The Rad51 paralogs are required for homologous recombination (HR) and the maintenance of genomic stability. The molecular mechanisms by which the five vertebrate Rad51 paralogs regulate HR and genomic integrity remain unclear. The Rad51 paralogs associate with one another in two distinct complexes: Rad51B-Rad51C-Rad51D-XRCC2 (BCDX2) and Rad51C-XRCC3 (CX3). We find that the BCDX2 and CX3 complex act at different stages of the HR pathway. In response to DNA damage, the BCDX2 complex acts downstream of BRCA2 recruitment, but upstream of Rad51 recruitment. In contrast, the CX3 complex acts downstream of Rad51 recruitment, but still have a marked impact on the measured frequency of homologous recombination. Both complexes are epistatic with BRCA2 and synthetically lethal with Rad52. We conclude that human Rad51 paralogs facilitate the BRCA2-Rad51 dependent homologous recombination at different stages in the pathway and function independently of Rad52.

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Available from: Jarin Chun, Aug 28, 2015
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    • "Our observations, together with previously reported findings, suggest that Rad51 paralogs perform two distinct functions to promote HR: they protect Rad51-ssDNA filaments against disruption by antirecombinases (Liu et al., 2011a) and directly stimulate the intrinsic recombinase activity of Rad51 by remodeling pre-synaptic filaments to an active, ''open,'' flexible, and stable conformation primed for homology search and strand invasion . Importantly, the mechanism we have discovered for the Rad51 paralogs in stimulating HR is distinct from that proposed for other positive regulators of HR, which are epistatic to Rad51 paralogs, including BRCA2 and Rad54 (Chun et al., 2013; Jensen et al., 2010, 2013; Liu et al., 2010; Solinger et al., 2002; Thorslund et al., 2010). We therefore propose a model (Figure 7I) for HR, in photobleaches; histogram of FRET values collected from all molecules with a Gaussian fit are shown in red, where x 0 is the mean FRET, s is the distribution width, and c 2 quantifies the quality of the fit. "
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    ABSTRACT: Repair of DNA double strand breaks by homologous recombination (HR) is initiated by Rad51 filament nucleation on single-stranded DNA (ssDNA), which catalyzes strand exchange with homologous duplex DNA. BRCA2 and the Rad51 paralogs are tumor suppressors and critical mediators of Rad51. To gain insight into Rad51 paralog function, we investigated a heterodimeric Rad51 paralog complex, RFS-1/RIP-1, and uncovered the molecular basis by which Rad51 paralogs promote HR. Unlike BRCA2, which nucleates RAD-51-ssDNA filaments, RFS-1/RIP-1 binds and remodels pre-synaptic filaments to a stabilized, "open," and flexible conformation, in which the ssDNA is more accessible to nuclease digestion and RAD-51 dissociation rate is reduced. Walker box mutations in RFS-1, which abolish filament remodeling, fail to stimulate RAD-51 strand exchange activity, demonstrating that remodeling is essential for RFS-1/RIP-1 function. We propose that Rad51 paralogs stimulate HR by remodeling the Rad51 filament, priming it for strand exchange with the template duplex. Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.
    Cell 07/2015; 162(2):271-286. DOI:10.1016/j.cell.2015.06.015 · 33.12 Impact Factor
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    • "Our observations, together with previously reported findings, suggest that Rad51 paralogs perform two distinct functions to promote HR: they protect Rad51-ssDNA filaments against disruption by antirecombinases (Liu et al., 2011a) and directly stimulate the intrinsic recombinase activity of Rad51 by remodeling pre-synaptic filaments to an active, ''open,'' flexible, and stable conformation primed for homology search and strand invasion . Importantly, the mechanism we have discovered for the Rad51 paralogs in stimulating HR is distinct from that proposed for other positive regulators of HR, which are epistatic to Rad51 paralogs, including BRCA2 and Rad54 (Chun et al., 2013; Jensen et al., 2010, 2013; Liu et al., 2010; Solinger et al., 2002; Thorslund et al., 2010). We therefore propose a model (Figure 7I) for HR, in photobleaches; histogram of FRET values collected from all molecules with a Gaussian fit are shown in red, where x 0 is the mean FRET, s is the distribution width, and c 2 quantifies the quality of the fit. "
    Cell 07/2015; 162:271-286. · 33.12 Impact Factor
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    • "It has also been proposed that CX3 functions in late stages of HR pathway, resolving Holidays junctions (Liu et al., 2004, 2007; Sharan and Kuznetsov, 2007). Recently, Chun et al. (2013) have demonstrated in human cells that in response to DNA damage, BCDX2 and CX3 complexes act upstream and downstream of RAD51 recruitment, respectively, and both are epistatic with BRCA2. "
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    ABSTRACT: Meiotic recombination plays a critical role in achieving accurate chromosome segregation and increasing genetic diversity. Many studies, mostly in yeast, have provided important insights into the coordination and interplay between the proteins involved in the homologous recombination pathway, especially the recombinase RAD51 and the meiosis-specific DMC1. Here we summarize the current progresses on the function of both recombinases and the CX3 complex encoded by AtRAD51 paralogs, in the plant model species Arabidopsis thaliana. Similarities and differences respect to the function of these proteins in other organisms are also indicated.
    Frontiers in Plant Science 02/2014; 5:23. DOI:10.3389/fpls.2014.00023 · 3.95 Impact Factor
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