| 1. |
- Banyai, Gabor, et al.
(author)
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Cyclin C influences the timing of mitosis in fission yeast.
- 2017
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In: Molecular biology of the cell. - 1939-4586. ; 28:13, s. 1738-1744
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Journal article (peer-reviewed)abstract
- The multiprotein Mediator complex is required for the regulated transcription of nearly all RNA polymerase II-dependent genes. Mediator contains the Cdk8 regulatory subcomplex, which directs periodic transcription and influences cell cycle progression in fission yeast. Here we investigate the role of CycC, the cognate cyclin partner of Cdk8, in cell cycle control. Previous reports suggested that CycC interacts with other cellular Cdks, but a fusion of CycC to Cdk8 reported here did not cause any obvious cell cycle phenotypes. We find that Cdk8 and CycC interactions are stabilized within the Mediator complex and the activity of Cdk8-CycC is regulated by other Mediator components. Analysis of a mutant yeast strain reveals that CycC, together with Cdk8, primarily affects M-phase progression but mutations that release Cdk8 from CycC control also affect timing of entry into S phase.
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| 2. |
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| 3. |
- Khorosjutina, Olga
(author)
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Fission yeast mediator complex and its role in transcriptional regulation
- 2011
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Doctoral thesis (other academic/artistic)abstract
- Mediator is an evolutionary conserved co-activator complex that regulates transcription of protein encoding genes in eukaryotes. This multiprotein complex was first identified in budding yeast and shown to be indispensable for RNA polymerase II (pol II) dependent transcription. Mediator is a transducer of regulatory signals from gene specific transcription factors to the general transcription machinery. Mediator has both activating and repressive functions, but the regulatory mechanisms are not yet completely understood. In our work, we have used a biochemical approach and identified four proteins, Med12, Med13, Cdk8, and CycC, as subunits of a repressive kinase module present in the Schizosaccharomyces pombe Mediator complex. Taking advantage of a reconstituted in vitro transcription system, we have tried to address the mechanism of transcriptional repression by this subcomplex. We have also addressed the function of the Med15 Mediator subunit, which has been characterized previously in other species. In Paper I we isolated a new form of the S. pombe Mediator complex to near homogeneity and denoted this complex Large (L-) Mediator. The L- Mediator contains four additional subunit not previously identified in the S. pombe core Mediator complex, but present in many of the large Mediator complexes isolated from higher eukaryotes. In contrast to the core Mediator complex, L-Mediator does not interact with pol II. Based on our biochemistry findings and bioinformatic analysis, our data suggest that Med12, Med13, Cdk8, and CycC form evolutionally conserved kinase module. In Paper II we developed an in vitro transcription system reconstituted with all the general transcription factors purified to near homogeneity, in either native or recombinant form. Fission yeast pol II assisted by TFIIB, TFIIF, TFIIE, TFIIH, and budding yeast TBP could initiate transcription from the S. pombe adh1 promoter in vitro. We found that addition of the core Mediator in complex with pol II could stimulate basal transcription, while L-Mediator suppressed transcription initiation in a dose dependent manner. Based on our findings, we proposed a model explaining the repressive function of L-Mediator. In Paper III we systematically addressed the structural organization of kinase module of L-Mediator. We identified Med13 as a key architectural subunit, anchoring the kinase module to the rest of the Mediator complex. Med13 was sufficient and necessary to occlude pol II from binding to Mediator, whereas deletion of Cdk8 and CycC did not affect Mediator association with pol II. In Paper IV we identified two new S. pombe Mediator components. The evolutionary conserved Med15 subunit associated with the chromatin remodeling protein Hrp1 and formed transient interactions with the S. pombe L-Mediator complex. Genome wide association data demonstrated Med15 association with a distinct subset of Hrp1 bound gene promoters.
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| 4. |
- Steglich, Babett, et al.
(author)
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The Fun30 Chromatin Remodeler Fft3 Controls Nuclear Organization and Chromatin Structure of Insulators and Subtelomeres in Fission Yeast
- 2015
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In: PLoS Genetics. - : Public Library of Science (PLoS). - 1553-7390 .- 1553-7404. ; 11:3, s. e1005101-
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Journal article (peer-reviewed)abstract
- In eukaryotic cells, local chromatin structure and chromatin organization in the nucleus both influence transcriptional regulation. At the local level, the Fun30 chromatin remodeler Fft3 is essential for maintaining proper chromatin structure at centromeres and subtelomeres in fission yeast. Using genome-wide mapping and live cell imaging, we show that this role is linked to controlling nuclear organization of its targets. In fft3? cells, subtelomeres lose their association with the LEM domain protein Man1 at the nuclear periphery and move to the interior of the nucleus. Furthermore, genes in these domains are upregulated and active chromatin marks increase. Fft3 is also enriched at retrotransposon-derived long terminal repeat (LTR) elements and at tRNA genes. In cells lacking Fft3, these sites lose their peripheral positioning and show reduced nucleosome occupancy. We propose that Fft3 has a global role in mediating association between specific chromatin domains and the nuclear envelope.
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| 5. |
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| 6. |
- Walfridsson, Julian, et al.
(author)
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A genome-wide role for CHD remodelling factors and Nap1 in nucleosome disassembly
- 2007
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In: EMBO Journal. - : Wiley. - 0261-4189 .- 1460-2075. ; 26:12, s. 2868-2879
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Journal article (peer-reviewed)abstract
- Chromatin remodelling factors and histone chaperones were previously shown to cooperatively affect nucleosome assembly and disassembly processes in vitro. Here, we show that Schizosaccharomyces pombe CHD remodellers, the Hrp1 and Hrp3 paralogs physically interact with the histone chaperone Nap1. Genome- wide analysis of Hrp1, Hrp3 and Nap1 occupancy, combined with nucleosome density measurements revealed that the CHD factors and Nap1 colocalized in particular to promoter regions where they remove nucleosomes near the transcriptional start site. Hrp1 and Hrp3 also regulate nucleosome density in coding regions, where they have redundant roles to stimulate transcription. Previously, DNA replication-dependent and -independent nucleosome disassembly processes have been described. We found that nucleosome density increased in the hrp1 mutant in the absence of DNA replication. Finally, regions where nucleosome density increased in hrp1, hrp3 and nap1 mutants also showed nucleosome density and histone modification changes in HDAC and HAT mutants. Thus, this study revealed an important in vivo role for CHD remodellers and Nap1 in nucleosome disassembly at promoters and coding regions, which are linked to changes in histone acetylation.
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