Dataset Information

The Shu complex interacts with Rad51 through the Rad51 paralogues Rad55-Rad57 to mediate error-free recombination.

ABSTRACT: The Saccharomyces cerevisiae Shu complex, consisting of Shu1, Shu2, Csm2 and Psy3, promotes error-free homologous recombination (HR) by an unknown mechanism. Recent structural analysis of two Shu proteins, Csm2 and Psy3, has revealed that these proteins are Rad51 paralogues and mediate DNA binding of this complex. We show in vitro that the Csm2-Psy3 heterodimer preferentially binds synthetic forked DNA or 3'-DNA overhang substrates resembling structures used during HR in vivo. We find that Csm2 interacts with Rad51 and the Rad51 paralogues, the Rad55-Rad57 heterodimer and that the Shu complex functions in the same epistasis group as Rad55-Rad57. Importantly, Csm2's interaction with Rad51 is dependent on Rad55, whereas Csm2's interaction with Rad55 occurs independently of Rad51. Consistent with the Shu complex containing Rad51 paralogues, the methyl methanesulphonate sensitivity of Csm2 is exacerbated at colder temperatures. Furthermore, Csm2 and Psy3 are needed for efficient recruitment of Rad55 to DNA repair foci after DNA damage. Finally, we observe that the Shu complex preferentially promotes Rad51-dependent homologous recombination over Rad51-independent repair. Our data suggest a model in which Csm2-Psy3 recruit the Shu complex to HR substrates, where it interacts with Rad51 through Rad55-Rad57 to stimulate Rad51 filament assembly and stability, promoting error-free repair.

SUBMITTER: Godin S

PROVIDER: S-EPMC3632125 | biostudies-literature | 2013 Apr

REPOSITORIES: biostudies-literature

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The Shu complex interacts with Rad51 through the Rad51 paralogues Rad55-Rad57 to mediate error-free recombination.

Godin Stephen S Wier Adam A Kabbinavar Faiz F Bratton-Palmer Dominique S DS Ghodke Harshad H Van Houten Bennett B VanDemark Andrew P AP Bernstein Kara A KA

Nucleic acids research 20130304 8

The Saccharomyces cerevisiae Shu complex, consisting of Shu1, Shu2, Csm2 and Psy3, promotes error-free homologous recombination (HR) by an unknown mechanism. Recent structural analysis of two Shu proteins, Csm2 and Psy3, has revealed that these proteins are Rad51 paralogues and mediate DNA binding of this complex. We show in vitro that the Csm2-Psy3 heterodimer preferentially binds synthetic forked DNA or 3'-DNA overhang substrates resembling structures used during HR in vivo. We find that Csm2 ...[more]

PMID: 23460207

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Project description:Homologous recombination is a high-fidelity DNA repair pathway. Besides a critical role in accurate chromosome segregation during meiosis, recombination functions in DNA repair and in the recovery of stalled or broken replication forks to ensure genomic stability. In contrast, inappropriate recombination contributes to genomic instability, leading to loss of heterozygosity, chromosome rearrangements and cell death. The RecA/UvsX/RadA/Rad51 family of proteins catalyses the signature reactions of recombination, homology search and DNA strand invasion. Eukaryotes also possess Rad51 paralogues, whose exact role in recombination remains to be defined. Here we show that the Saccharomyces cerevisiae Rad51 paralogues, the Rad55-Rad57 heterodimer, counteract the antirecombination activity of the Srs2 helicase. The Rad55-Rad57 heterodimer associates with the Rad51-single-stranded DNA filament, rendering it more stable than a nucleoprotein filament containing Rad51 alone. The Rad51-Rad55-Rad57 co-filament resists disruption by the Srs2 antirecombinase by blocking Srs2 translocation, involving a direct protein interaction between Rad55-Rad57 and Srs2. Our results demonstrate an unexpected role of the Rad51 paralogues in stabilizing the Rad51 filament against a biologically important antagonist, the Srs2 antirecombination helicase. The biological significance of this mechanism is indicated by a complete suppression of the ionizing radiation sensitivity of rad55 or rad57 mutants by concomitant deletion of SRS2, as expected for biological antagonists. We propose that the Rad51 presynaptic filament is a meta-stable reversible intermediate, whose assembly and disassembly is governed by the balance between Rad55-Rad57 and Srs2, providing a key regulatory mechanism controlling the initiation of homologous recombination. These data provide a paradigm for the potential function of the human RAD51 paralogues, which are known to be involved in cancer predisposition and human disease.

Project description:In cells lacking telomerase, telomeres shorten progressively during each cell division due to incomplete end-replication. When the telomeres become very short, cells enter a state that blocks cell division, termed senescence. A subset of these cells can overcome senescence and maintain their telomeres using telomerase-independent mechanisms. In Saccharomyces cerevisiae, these cells are called 'survivors' and are dependent on Rad52-dependent homologous recombination and Pol32-dependent break-induced replication. There are two main types of survivors: type I and type II. The type I survivors require Rad51 and maintain telomeres by amplification of subtelomeric elements, while the type II survivors are Rad51-independent, but require the MRX complex and Sgs1 to amplify the C1-3A/TG1-3 telomeric sequences. Rad52, Pol32, Rad51, and Sgs1 are also important to prevent accelerated senescence, indicating that recombination processes are important at telomeres even before the formation of survivors. The Shu complex, which consists of Shu1, Shu2, Psy3, and Csm2, promotes Rad51-dependent homologous recombination and has been suggested to be important for break-induced replication. It also promotes the formation of recombination intermediates that are processed by the Sgs1-Top3-Rmi1 complex, as mutations in the SHU genes can suppress various sgs1, top3, and rmi1 mutant phenotypes. Given the importance of recombination processes during senescence and survivor formation, and the involvement of the Shu complex in many of the same processes during DNA repair, we hypothesized that the Shu complex may also have functions at telomeres. Surprisingly, we find that this is not the case: the Shu complex does not affect the rate of senescence, does not influence survivor formation, and deletion of SHU1 does not suppress the rapid senescence and type II survivor formation defect of a telomerase-negative sgs1 mutant. Altogether, our data suggest that the Shu complex is not important for recombination processes at telomeres.

Dataset Information

The Shu complex interacts with Rad51 through the Rad51 paralogues Rad55-Rad57 to mediate error-free recombination.

Publications

The Shu complex interacts with Rad51 through the Rad51 paralogues Rad55-Rad57 to mediate error-free recombination.

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