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The exosome Associates Cotranscriptionally with the Nascent Pre-mRNP through Interactions with Heterogeneous Nuclear Ribonucleoproteins
Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
Stockholm University, Faculty of Science, Department of Molecular Biology and Functional Genomics.
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2009 (English)In: Molecular Biology of the Cell, ISSN 1059-1524, E-ISSN 1939-4586, Vol. 20, no 15, 3459-3470 p.Article in journal (Refereed) Published
Abstract [en]

Eukaryotic cells have evolved quality control mechanisms to degrade aberrant mRNA molecules and prevent the synthesis of defective proteins that could be deleterious for the cell. The exosome, a protein complex with ribonuclease activity, is a key player in quality control. An early quality checkpoint takes place cotranscriptionally but little is known about the molecular mechanisms by which the exosome is recruited to the transcribed genes. Here we study the core exosome subunit Rrp4 in two insect model systems, Chironomus and Drosophila. We show that a significant fraction of Rrp4 is associated with the nascent pre-mRNPs and that a specific mRNA-binding protein, Hrp59/hnRNP M, interacts in vivo with multiple exosome subunits. Depletion of Hrp59 by RNA interference reduces the levels of Rrp4 at transcription sites, which suggests that Hrp59 is needed for the exosome to stably interact with nascent pre-mRNPs. Our results lead to a revised mechanistic model for cotranscriptional quality control in which the exosome is constantly recruited to newly synthesized RNAs through direct interactions with specific hnRNP proteins.

Place, publisher, year, edition, pages
2009. Vol. 20, no 15, 3459-3470 p.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:su:diva-35089DOI: 10.1091/mbc.E09-01-0079ISI: 000268545300002OAI: oai:DiVA.org:su-35089DiVA: diva2:286380
Available from: 2010-01-14 Created: 2010-01-14 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Characterization of RNA exosome in Insect Cells: Role in mRNA Surveillance
Open this publication in new window or tab >>Characterization of RNA exosome in Insect Cells: Role in mRNA Surveillance
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The exosome, an evolutionarily conserved protein complex with exoribonucleolytic activity, is one of the key players in mRNA quality control. Little is known about the functions of the exosome in metazoans. We have studied the role of the exosome in nuclear mRNA surveillance using Chironomus tentans and Drosophila melanogaster as model systems. Studies of the exosome subunits Rrp4 and Rrp6 revealed that both proteins are associated with transcribed genes and nascent pre-mRNPs in C. tentans. We have shown that several exosome subunits interact in vivo with the mRNA-binding protein Hrp59/hnRNP M, and that depleting Hrp59 in D. melanogaster S2 cells by RNAi leads to reduced levels of Rrp4 at the transcription sites. Our results on Rrp4 suggest a model for cotranscriptional quality control in which the exosome is constantly recruited to nascent mRNAs through interactions with specific hnRNP proteins. Moreover, we show that Rrp6 interacts with mRNPs in transit from the gene to the nuclear pore complex, where it is released during early stages of nucleo-cytoplasmic translocation. Furthermore, we show that Rrp6 is enriched in discrete nuclear bodies in the salivary glands of C. tentans and D. melanogaster. In C. tentans, the Rrp6-rich nuclear bodies colocalize with SUMO. We have also constructed D. melanogaster S2 cells expressing human b-globin genes, with either wild type of mutated splice sites, and we have studied the mechanisms by which the cells react to pre-mRNA processing defects. Our results indicate that two surveillance responses operate co-transcriptionally in S2 cells. One requires Rrp6 and retains defective mRNAs at the transcription site. The other one reduces the synthesis of the defective transcripts through a mechanism that involves histone modifications. These observations support the view that multiple mechanisms contribute to co-transcriptional surveillance in insects.

Place, publisher, year, edition, pages
Stockholm: Department of Molecular Biology and Functional Genomics, Stockholm University, 2011. 69 p.
Keyword
cell nucleus, nuclear bodies, mRNA surveillance, cotranscriptional assembly, Rrp6, Rrp4, mRNP
National Category
Biochemistry and Molecular Biology
Research subject
Molecular Biology
Identifiers
urn:nbn:se:su:diva-52127 (URN)978-91-7447-208-0 (ISBN)
Public defence
2011-02-11, De Geer-salen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 10:00 (English)
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Note
At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript. Available from: 2011-01-20 Created: 2011-01-13 Last updated: 2011-01-13Bibliographically approved

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Hessle, ViktoriaBjörk, PetraMaddalo, GianlucaIlag, LeopoldVisa, Neus
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