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Gaspary A, Laureau R, Dyatel A, Dursuk G, Simon Y, Berchowitz LE. Rie1 and Sgn1 form an RNA-binding complex that enforces the meiotic entry cell fate decision. J Cell Biol 2023; 222:e202302074. [PMID: 37638885 PMCID: PMC10460998 DOI: 10.1083/jcb.202302074] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2023] [Revised: 06/28/2023] [Accepted: 08/08/2023] [Indexed: 08/29/2023] Open
Abstract
Budding yeast cells have the capacity to adopt few but distinct physiological states depending on environmental conditions. Vegetative cells proliferate rapidly by budding while spores can survive prolonged periods of nutrient deprivation and/or desiccation. Whether or not a yeast cell will enter meiosis and sporulate represents a critical decision that could be lethal if made in error. Most cell fate decisions, including those of yeast, are understood as being triggered by the activation of master transcription factors. However, mechanisms that enforce cell fates posttranscriptionally have been more difficult to attain. Here, we perform a forward genetic screen to determine RNA-binding proteins that affect meiotic entry at the posttranscriptional level. Our screen revealed several candidates with meiotic entry phenotypes, the most significant being RIE1, which encodes an RRM-containing protein. We demonstrate that Rie1 binds RNA, is associated with the translational machinery, and acts posttranscriptionally to enhance protein levels of the master transcription factor Ime1 in sporulation conditions. We also identified a physical binding partner of Rie1, Sgn1, which is another RRM-containing protein that plays a role in timely Ime1 expression. We demonstrate that these proteins act independently of cell size regulation pathways to promote meiotic entry. We propose a model explaining how constitutively expressed RNA-binding proteins, such as Rie1 and Sgn1, can act in cell fate decisions both as switch-like enforcers and as repressors of spurious cell fate activation.
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Affiliation(s)
- Alec Gaspary
- Department of Genetics and Development, Hammer Health Sciences Center, Columbia University Irving Medical Center, New York, NY, USA
| | - Raphaelle Laureau
- Department of Genetics and Development, Hammer Health Sciences Center, Columbia University Irving Medical Center, New York, NY, USA
| | - Annie Dyatel
- Department of Genetics and Development, Hammer Health Sciences Center, Columbia University Irving Medical Center, New York, NY, USA
| | - Gizem Dursuk
- Department of Genetics and Development, Hammer Health Sciences Center, Columbia University Irving Medical Center, New York, NY, USA
| | - Yael Simon
- Department of Genetics and Development, Hammer Health Sciences Center, Columbia University Irving Medical Center, New York, NY, USA
| | - Luke E. Berchowitz
- Department of Genetics and Development, Hammer Health Sciences Center, Columbia University Irving Medical Center, New York, NY, USA
- Taub Institute for Research on Alzheimer’s and the Aging Brain, New York, NY, USA
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2
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Gastelum S, Michael AF, Bolger TA. Saccharomyces cerevisiae as a research tool for RNA-mediated human disease. WILEY INTERDISCIPLINARY REVIEWS. RNA 2023; 15:e1814. [PMID: 37671427 DOI: 10.1002/wrna.1814] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2022] [Revised: 07/25/2023] [Accepted: 07/26/2023] [Indexed: 09/07/2023]
Abstract
The budding yeast, Saccharomyces cerevisiae, has been used for decades as a powerful genetic tool to study a broad spectrum of biological topics. With its ease of use, economic utility, well-studied genome, and a highly conserved proteome across eukaryotes, it has become one of the most used model organisms. Due to these advantages, it has been used to study an array of complex human diseases. From broad, complex pathological conditions such as aging and neurodegenerative disease to newer uses such as SARS-CoV-2, yeast continues to offer new insights into how cellular processes are affected by disease and how affected pathways might be targeted in therapeutic settings. At the same time, the roles of RNA and RNA-based processes have become increasingly prominent in the pathology of many of these same human diseases, and yeast has been utilized to investigate these mechanisms, from aberrant RNA-binding proteins in amyotrophic lateral sclerosis to translation regulation in cancer. Here we review some of the important insights that yeast models have yielded into the molecular pathology of complex, RNA-based human diseases. This article is categorized under: RNA in Disease and Development > RNA in Disease.
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Affiliation(s)
- Stephanie Gastelum
- Department of Molecular and Cellular Biology, University of Arizona, Tucson, Arizona, USA
| | - Allison F Michael
- Department of Biochemistry and Molecular Biology, University of Georgia, Athens, GA, USA
| | - Timothy A Bolger
- Department of Biochemistry and Molecular Biology, University of Georgia, Athens, GA, USA
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3
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Rodríguez‐Molina JB, Turtola M. Birth of a poly(A) tail: mechanisms and control of mRNA polyadenylation. FEBS Open Bio 2023; 13:1140-1153. [PMID: 36416579 PMCID: PMC10315857 DOI: 10.1002/2211-5463.13528] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2022] [Revised: 11/17/2022] [Accepted: 11/22/2022] [Indexed: 11/24/2022] Open
Abstract
During their synthesis in the cell nucleus, most eukaryotic mRNAs undergo a two-step 3'-end processing reaction in which the pre-mRNA is cleaved and released from the transcribing RNA polymerase II and a polyadenosine (poly(A)) tail is added to the newly formed 3'-end. These biochemical reactions might appear simple at first sight (endonucleolytic RNA cleavage and synthesis of a homopolymeric tail), but their catalysis requires a multi-faceted enzymatic machinery, the cleavage and polyadenylation complex (CPAC), which is composed of more than 20 individual protein subunits. The activity of CPAC is further orchestrated by Poly(A) Binding Proteins (PABPs), which decorate the poly(A) tail during its synthesis and guide the mRNA through subsequent gene expression steps. Here, we review the structure, molecular mechanism, and regulation of eukaryotic mRNA 3'-end processing machineries with a focus on the polyadenylation step. We concentrate on the CPAC and PABPs from mammals and the budding yeast, Saccharomyces cerevisiae, because these systems are the best-characterized at present. Comparison of their functions provides valuable insights into the principles of mRNA 3'-end processing.
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Affiliation(s)
| | - Matti Turtola
- Department of Life TechnologiesUniversity of TurkuFinland
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4
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Reynaud K, McGeachy AM, Noble D, Meacham ZA, Ingolia NT. Surveying the global landscape of post-transcriptional regulators. Nat Struct Mol Biol 2023; 30:740-752. [PMID: 37231154 PMCID: PMC10279529 DOI: 10.1038/s41594-023-00999-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2021] [Accepted: 04/17/2023] [Indexed: 05/27/2023]
Abstract
Numerous proteins regulate gene expression by modulating mRNA translation and decay. To uncover the full scope of these post-transcriptional regulators, we conducted an unbiased survey that quantifies regulatory activity across the budding yeast proteome and delineates the protein domains responsible for these effects. Our approach couples a tethered function assay with quantitative single-cell fluorescence measurements to analyze ~50,000 protein fragments and determine their effects on a tethered mRNA. We characterize hundreds of strong regulators, which are enriched for canonical and unconventional mRNA-binding proteins. Regulatory activity typically maps outside the RNA-binding domains themselves, highlighting a modular architecture that separates mRNA targeting from post-transcriptional regulation. Activity often aligns with intrinsically disordered regions that can interact with other proteins, even in core mRNA translation and degradation factors. Our results thus reveal networks of interacting proteins that control mRNA fate and illuminate the molecular basis for post-transcriptional gene regulation.
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Affiliation(s)
- Kendra Reynaud
- California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, CA, USA
| | - Anna M McGeachy
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA, USA
| | - David Noble
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA, USA
| | - Zuriah A Meacham
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA, USA
| | - Nicholas T Ingolia
- California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, CA, USA.
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA, USA.
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5
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Hallacli E, Kayatekin C, Nazeen S, Wang XH, Sheinkopf Z, Sathyakumar S, Sarkar S, Jiang X, Dong X, Di Maio R, Wang W, Keeney MT, Felsky D, Sandoe J, Vahdatshoar A, Udeshi ND, Mani DR, Carr SA, Lindquist S, De Jager PL, Bartel DP, Myers CL, Greenamyre JT, Feany MB, Sunyaev SR, Chung CY, Khurana V. The Parkinson's disease protein alpha-synuclein is a modulator of processing bodies and mRNA stability. Cell 2022; 185:2035-2056.e33. [PMID: 35688132 DOI: 10.1016/j.cell.2022.05.008] [Citation(s) in RCA: 49] [Impact Index Per Article: 24.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2021] [Revised: 04/05/2022] [Accepted: 05/06/2022] [Indexed: 12/13/2022]
Abstract
Alpha-synuclein (αS) is a conformationally plastic protein that reversibly binds to cellular membranes. It aggregates and is genetically linked to Parkinson's disease (PD). Here, we show that αS directly modulates processing bodies (P-bodies), membraneless organelles that function in mRNA turnover and storage. The N terminus of αS, but not other synucleins, dictates mutually exclusive binding either to cellular membranes or to P-bodies in the cytosol. αS associates with multiple decapping proteins in close proximity on the Edc4 scaffold. As αS pathologically accumulates, aberrant interaction with Edc4 occurs at the expense of physiologic decapping-module interactions. mRNA decay kinetics within PD-relevant pathways are correspondingly disrupted in PD patient neurons and brain. Genetic modulation of P-body components alters αS toxicity, and human genetic analysis lends support to the disease-relevance of these interactions. Beyond revealing an unexpected aspect of αS function and pathology, our data highlight the versatility of conformationally plastic proteins with high intrinsic disorder.
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Affiliation(s)
- Erinc Hallacli
- Ann Romney Center for Neurologic Diseases, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA; Division of Movement Disorders, Department of Neurology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA; Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA
| | - Can Kayatekin
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA
| | - Sumaiya Nazeen
- Ann Romney Center for Neurologic Diseases, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA; Division of Movement Disorders, Department of Neurology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA; Department of Biomedical Informatics, Harvard Medical School, Boston, MA 02115, USA; Division of Genetics, Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115
| | - Xiou H Wang
- Ann Romney Center for Neurologic Diseases, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA; Division of Movement Disorders, Department of Neurology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA
| | - Zoe Sheinkopf
- Ann Romney Center for Neurologic Diseases, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA; Division of Movement Disorders, Department of Neurology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA
| | - Shubhangi Sathyakumar
- Ann Romney Center for Neurologic Diseases, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA; Division of Movement Disorders, Department of Neurology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA
| | - Souvarish Sarkar
- Department of Pathology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA
| | - Xin Jiang
- Yumanity Therapeutics, Boston, MA 02135, USA
| | - Xianjun Dong
- Ann Romney Center for Neurologic Diseases, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA; Genomics and Bioinformatics Hub, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA; Aligning Science Across Parkinson's (ASAP) Collaborative Research Network, Chevy Chase, MD 20815, USA
| | - Roberto Di Maio
- Pittsburgh Institute for Neurodegenerative Diseases and Department of Neurology, Pittsburgh, PA 15213, USA
| | - Wen Wang
- Department of Computer Science and Engineering, University of Minnesota, Minneapolis, MN 55455, USA
| | - Matthew T Keeney
- Pittsburgh Institute for Neurodegenerative Diseases and Department of Neurology, Pittsburgh, PA 15213, USA
| | - Daniel Felsky
- Krembil Centre for Neuroinformatics and Department of Psychiatry, University of Toronto, Toronto, ON M5T 1R8, Canada; Department of Psychiatry, Temerty Faculty of Medicine, University of Toronto, 1 King's College Circle, Toronto, ON M5S 1A8, Canada; Division of Biostatistics, Dalla Lana School of Public Health, University of Toronto, 155 College Street, Toronto, ON M5T 3M7, Canada
| | - Jackson Sandoe
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA
| | - Aazam Vahdatshoar
- Ann Romney Center for Neurologic Diseases, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA; Division of Movement Disorders, Department of Neurology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA
| | | | - D R Mani
- Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA
| | - Steven A Carr
- Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA
| | - Susan Lindquist
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA; Howard Hughes Medical Institute, Cambridge, MA 02142, USA; Department of Biology, MIT, Cambridge, MA 02139, USA
| | - Philip L De Jager
- Center for Translational & Computational Neuroimmunology, Department of Neurology, Columbia University Irving Medical Center, New York, NY 10032, USA
| | - David P Bartel
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA; Howard Hughes Medical Institute, Cambridge, MA 02142, USA; Department of Biology, MIT, Cambridge, MA 02139, USA
| | - Chad L Myers
- Department of Computer Science and Engineering, University of Minnesota, Minneapolis, MN 55455, USA
| | - J Timothy Greenamyre
- Pittsburgh Institute for Neurodegenerative Diseases and Department of Neurology, Pittsburgh, PA 15213, USA
| | - Mel B Feany
- Department of Pathology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA
| | - Shamil R Sunyaev
- Department of Biomedical Informatics, Harvard Medical School, Boston, MA 02115, USA; Division of Genetics, Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115
| | | | - Vikram Khurana
- Ann Romney Center for Neurologic Diseases, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA; Division of Movement Disorders, Department of Neurology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA; Aligning Science Across Parkinson's (ASAP) Collaborative Research Network, Chevy Chase, MD 20815, USA; Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA; Harvard Stem Cell Institute, Cambridge, MA 02138, USA.
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6
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Characterization of the RNA-Binding Protein TcSgn1 in Trypanosoma cruzi. Microorganisms 2021; 9:microorganisms9050986. [PMID: 34063193 PMCID: PMC8147501 DOI: 10.3390/microorganisms9050986] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2021] [Revised: 04/23/2021] [Accepted: 04/27/2021] [Indexed: 11/24/2022] Open
Abstract
RNA-binding proteins (RBPs) participate in several steps of post-transcriptional regulation of gene expression, such as splicing, messenger RNA transport, mRNA localization, and translation. Gene-expression regulation in trypanosomatids occurs primarily at the post-transcriptional level, and RBPs play important roles in the process. Here, we characterized the RBP TcSgn1, which contains one RNA recognition motif (RRM). TcSgn1 is a close ortholog of yeast Saccharomyces cerevisiae protein ScSgn1, which plays a role in translational regulation in the cytoplasm. We found that TcSgn1 in Trypanosoma cruzi is localized in the nucleus in exponentially growing epimastigotes. By performing immunoprecipitation assays of TcSgn1, we identified hundreds of mRNAs associated with the protein, a significant fraction of them coding for nucleic acids binding, transcription, and endocytosis proteins. In addition, we show that TcSgn1 is capable of interacting directly with the poly(A) tail of the mRNAs. The study of parasites under nutritional stress showed that TcSgn1 was localized in cytoplasmic granules in addition to localizing in the nucleus. Similar to ScSgn1, we observed that TcSgn1 also interacts with the PABP1 protein, suggesting that this protein may play a role in regulating gene expression in T. cruzi. Taken together, our results show that RNA-binding protein TcSgn1 is part of ribonucleoprotein complexes associated with nuclear functions, stress response, and RNA metabolism.
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7
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Kühn U, Buschmann J, Wahle E. The nuclear poly(A) binding protein of mammals, but not of fission yeast, participates in mRNA polyadenylation. RNA (NEW YORK, N.Y.) 2017; 23:473-482. [PMID: 28096519 PMCID: PMC5340911 DOI: 10.1261/rna.057026.116] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2016] [Accepted: 01/04/2017] [Indexed: 05/22/2023]
Abstract
The nuclear poly(A) binding protein (PABPN1) has been suggested, on the basis of biochemical evidence, to play a role in mRNA polyadenylation by strongly increasing the processivity of poly(A) polymerase. While experiments in metazoans have tended to support such a role, the results were not unequivocal, and genetic data show that the S. pombe ortholog of PABPN1, Pab2, is not involved in mRNA polyadenylation. The specific model in which PABPN1 increases the rate of poly(A) tail elongation has never been examined in vivo. Here, we have used 4-thiouridine pulse-labeling to examine the lengths of newly synthesized poly(A) tails in human cells. Knockdown of PABPN1 strongly reduced the synthesis of full-length tails of ∼250 nucleotides, as predicted from biochemical data. We have also purified S. pombe Pab2 and the S. pombe poly(A) polymerase, Pla1, and examined their in vitro activities. Whereas PABPN1 strongly increases the activity of its cognate poly(A) polymerase in vitro, Pab2 was unable to stimulate Pla1 to any significant extent. Thus, in vitro and in vivo data are consistent in supporting a role of PABPN1 but not S. pombe Pab2 in the polyadenylation of mRNA precursors.
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Affiliation(s)
- Uwe Kühn
- Institute of Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, 06099 Halle, Germany
| | - Juliane Buschmann
- Institute of Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, 06099 Halle, Germany
| | - Elmar Wahle
- Institute of Biochemistry and Biotechnology, Martin Luther University Halle-Wittenberg, 06099 Halle, Germany
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8
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Delineating the structural blueprint of the pre-mRNA 3'-end processing machinery. Mol Cell Biol 2014; 34:1894-910. [PMID: 24591651 DOI: 10.1128/mcb.00084-14] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Processing of mRNA precursors (pre-mRNAs) by polyadenylation is an essential step in gene expression. Polyadenylation consists of two steps, cleavage and poly(A) synthesis, and requires multiple cis elements in the pre-mRNA and a megadalton protein complex bearing the two essential enzymatic activities. While genetic and biochemical studies remain the major approaches in characterizing these factors, structural biology has emerged during the past decade to help understand the molecular assembly and mechanistic details of the process. With structural information about more proteins and higher-order complexes becoming available, we are coming closer to obtaining a structural blueprint of the polyadenylation machinery that explains both how this complex functions and how it is regulated and connected to other cellular processes.
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9
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Howard A, Rogers AN. Role of translation initiation factor 4G in lifespan regulation and age-related health. Ageing Res Rev 2014; 13:115-24. [PMID: 24394551 DOI: 10.1016/j.arr.2013.12.008] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2013] [Revised: 12/18/2013] [Accepted: 12/23/2013] [Indexed: 01/04/2023]
Abstract
Inhibiting expression of eukaryotic translation initiation factor 4G (eIF4G) arrests normal development but extends lifespan when suppressed during adulthood. In addition to reducing overall translation, inhibition alters the stoichiometry of mRNA translation in favor of genes important for responding to stress and against those associated with growth and reproduction in C. elegans. In humans, aberrant expression of eIF4G is associated with certain forms of cancer and neurodegeneration. Here we review what is known about the roles of eIF4G in molecular, cellular, and organismal contexts. Also discussed are the gaps in understanding of this factor, particularly with regard to the roles of specific forms of expression in individual tissues and the importance of understanding eIF4G for development of potential therapeutic applications.
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10
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The human nuclear poly(a)-binding protein promotes RNA hyperadenylation and decay. PLoS Genet 2013; 9:e1003893. [PMID: 24146636 PMCID: PMC3798265 DOI: 10.1371/journal.pgen.1003893] [Citation(s) in RCA: 92] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2013] [Accepted: 09/05/2013] [Indexed: 12/05/2022] Open
Abstract
Control of nuclear RNA stability is essential for proper gene expression, but the mechanisms governing RNA degradation in mammalian nuclei are poorly defined. In this study, we uncover a mammalian RNA decay pathway that depends on the nuclear poly(A)-binding protein (PABPN1), the poly(A) polymerases (PAPs), PAPα and PAPγ, and the exosome subunits RRP6 and DIS3. Using a targeted knockdown approach and nuclear RNA reporters, we show that PABPN1 and PAPα, redundantly with PAPγ, generate hyperadenylated decay substrates that are recognized by the exosome and degraded. Poly(A) tail extension appears to be necessary for decay, as cordycepin treatment or point mutations in the PAP-stimulating domain of PABPN1 leads to the accumulation of stable transcripts with shorter poly(A) tails than controls. Mechanistically, these data suggest that PABPN1-dependent promotion of PAP activity can stimulate nuclear RNA decay. Importantly, efficiently exported RNAs are unaffected by this decay pathway, supporting an mRNA quality control function for this pathway. Finally, analyses of both bulk poly(A) tails and specific endogenous transcripts reveals that a subset of nuclear RNAs are hyperadenylated in a PABPN1-dependent fashion, and this hyperadenylation can be either uncoupled or coupled with decay. Our results highlight a complex relationship between PABPN1, PAPα/γ, and nuclear RNA decay, and we suggest that these activities may play broader roles in the regulation of human gene expression. In eukaryotes, mRNAs include a stretch of adenosine nucleotides at their 3′ end termed the poly(A) tail. In the cytoplasm, the poly(A) tail stimulates translation of the mRNA into protein, and protects the transcript from degradation. Evidence suggests that poly(A) tails may play distinct roles in RNA metabolism in the nucleus, but little is known about these functions and mechanisms. We show here that poly(A) tails can stimulate transcript decay in the nucleus, a function mediated by the ubiquitous nuclear poly(A) binding protein PABPN1. We find that PABPN1 is required for the degradation of a viral nuclear noncoding RNA as well as an inefficiently exported human mRNA. Importantly, the targeting of RNAs to this decay pathway requires the PABPN1 and poly(A) polymerase-dependent extension of the poly(A) tail. Nuclear transcripts with longer poly(A) tails are then selectively degraded by components of the nuclear exosome. These studies elucidate mechanisms that mammalian cells use to ensure proper mRNA “quality control” and may be important to regulate the expression of nuclear noncoding RNAs. Furthermore, our results suggest that the poly(A) tail has diverse and context-specific roles in gene expression.
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11
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Characterization of global gene expression during assurance of lifespan extension by caloric restriction in budding yeast. Exp Gerontol 2013; 48:1455-68. [PMID: 24126084 DOI: 10.1016/j.exger.2013.10.001] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2013] [Revised: 09/28/2013] [Accepted: 10/03/2013] [Indexed: 12/22/2022]
Abstract
Caloric restriction (CR) is the best-studied intervention known to delay aging and extend lifespan in evolutionarily distant organisms ranging from yeast to mammals in the laboratory. Although the effect of CR on lifespan extension has been investigated for nearly 80years, the molecular mechanisms of CR are still elusive. Consequently, it is important to understand the fundamental mechanisms of when and how lifespan is affected by CR. In this study, we first identified the time-windows during which CR assured cellular longevity by switching cells from culture media containing 2% or 0.5% glucose to water, which allows us to observe CR and non-calorically-restricted cells under the same conditions. We also constructed time-dependent gene expression profiles and selected 646 genes that showed significant changes and correlations with the lifespan-extending effect of CR. The positively correlated genes participated in transcriptional regulation, ribosomal RNA processing and nuclear genome stability, while the negatively correlated genes were involved in the regulation of several metabolic pathways, endoplasmic reticulum function, stress response and cell cycle progression. Furthermore, we discovered major upstream regulators of those significantly changed genes, including AZF1 (YOR113W), HSF1 (YGL073W) and XBP1 (YIL101C). Deletions of two genes, AZF1 and XBP1 (HSF1 is essential and was thus not tested), were confirmed to lessen the lifespan extension mediated by CR. The absence of these genes in the tor1Δ and ras2Δ backgrounds did show non-overlapping effects with regard to CLS, suggesting differences between the CR mechanism for Tor and Ras signaling.
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12
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Poly(A) tail-mediated gene regulation by opposing roles of Nab2 and Pab2 nuclear poly(A)-binding proteins in pre-mRNA decay. Mol Cell Biol 2013; 33:4718-31. [PMID: 24081329 DOI: 10.1128/mcb.00887-13] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The 3' end of most eukaryotic transcripts is decorated by poly(A)-binding proteins (PABPs), which influence the fate of mRNAs throughout gene expression. However, despite the fact that multiple PABPs coexist in the nuclei of most eukaryotes, how functional interplay between these nuclear PABPs controls gene expression remains unclear. By characterizing the ortholog of the Nab2/ZC3H14 zinc finger PABP in Schizosaccharomyces pombe, we show here that the two major fission yeast nuclear PABPs, Pab2 and Nab2, have opposing roles in posttranscriptional gene regulation. Notably, we find that Nab2 functions in gene-specific regulation in a manner opposite to that of Pab2. By studying the ribosomal-protein-coding gene rpl30-2, which is negatively regulated by Pab2 via a nuclear pre-mRNA decay pathway that depends on the nuclear exosome subunit Rrp6, we show that Nab2 promotes rpl30-2 expression by acting at the level of the unspliced pre-mRNA. Our data support a model in which Nab2 impedes Pab2/Rrp6-mediated decay by competing with Pab2 for polyadenylated transcripts in the nucleus. The opposing roles of Pab2 and Nab2 reveal that interplay between nuclear PABPs can influence gene regulation.
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13
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Mallet PL, Bachand F. A Proline-Tyrosine Nuclear Localization Signal (PY-NLS) Is Required for the Nuclear Import of Fission Yeast PAB2, but Not of Human PABPN1. Traffic 2013; 14:282-94. [DOI: 10.1111/tra.12036] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2012] [Revised: 12/20/2012] [Accepted: 12/26/2012] [Indexed: 12/27/2022]
Affiliation(s)
- Pierre-Luc Mallet
- RNA Group, Department of Biochemistry; Université de Sherbrooke; Sherbrooke; QC; Canada
| | - François Bachand
- RNA Group, Department of Biochemistry; Université de Sherbrooke; Sherbrooke; QC; Canada
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14
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Chritton JJ, Wickens M. A role for the poly(A)-binding protein Pab1p in PUF protein-mediated repression. J Biol Chem 2011; 286:33268-78. [PMID: 21768112 DOI: 10.1074/jbc.m111.264572] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
PUF proteins regulate translation and mRNA stability throughout eukaryotes. Using a cell-free translation assay, we examined the mechanisms of translational repression of PUF proteins in the budding yeast Saccharomyces cerevisiae. We demonstrate that the poly(A)-binding protein Pab1p is required for PUF-mediated translational repression for two distantly related PUF proteins: S. cerevisiae Puf5p and Caenorhabditis elegans FBF-2. Pab1p interacts with oligo(A) tracts in the HO 3'-UTR, a target of Puf5p, to dramatically enhance the efficiency of Puf5p repression. Both the Pab1p ability to activate translation and interact with eukaryotic initiation factor 4G (eIF4G) were required to observe maximal repression by Puf5p. Repression was also more efficient when Pab1p was bound in close proximity to Puf5p. Puf5p may disrupt translation initiation by interfering with the interaction between Pab1p and eIF4G. Finally, we demonstrate two separable mechanisms of translational repression employed by Puf5p: a Pab1p-dependent mechanism and a Pab1p-independent mechanism.
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Affiliation(s)
- Jacqueline J Chritton
- Department of Genetics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
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Eckmann CR, Rammelt C, Wahle E. Control of poly(A) tail length. WILEY INTERDISCIPLINARY REVIEWS-RNA 2010; 2:348-61. [PMID: 21957022 DOI: 10.1002/wrna.56] [Citation(s) in RCA: 186] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Poly(A) tails have long been known as stable 3' modifications of eukaryotic mRNAs, added during nuclear pre-mRNA processing. It is now appreciated that this modification is much more diverse: A whole new family of poly(A) polymerases has been discovered, and poly(A) tails occur as transient destabilizing additions to a wide range of different RNA substrates. We review the field from the perspective of poly(A) tail length. Length control is important because (1) poly(A) tail shortening from a defined starting point acts as a timer of mRNA stability, (2) changes in poly(A) tail length are used for the purpose of translational regulation, and (3) length may be the key feature distinguishing between the stabilizing poly(A) tails of mRNAs and the destabilizing oligo(A) tails of different unstable RNAs. The mechanism of length control during nuclear processing of pre-mRNAs is relatively well understood and is based on the changes in the processivity of poly(A) polymerase induced by two RNA-binding proteins. Developmentally regulated poly(A) tail extension also generates defined tails; however, although many of the proteins responsible are known, the reaction is not understood mechanistically. Finally, destabilizing oligoadenylation does not appear to have inherent length control. Rather, average tail length results from the balance between polyadenylation and deadenylation.
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Affiliation(s)
- Christian R Eckmann
- Max-Planck-Institute of Molecular Cell Biology and Genetics, Dresden, Germany
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Lemay JF, D'Amours A, Lemieux C, Lackner DH, St-Sauveur VG, Bähler J, Bachand F. The nuclear poly(A)-binding protein interacts with the exosome to promote synthesis of noncoding small nucleolar RNAs. Mol Cell 2010; 37:34-45. [PMID: 20129053 DOI: 10.1016/j.molcel.2009.12.019] [Citation(s) in RCA: 91] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2009] [Revised: 08/11/2009] [Accepted: 11/09/2009] [Indexed: 11/19/2022]
Abstract
Poly(A)-binding proteins (PABPs) are important to eukaryotic gene expression. In the nucleus, the PABP PABPN1 is thought to function in polyadenylation of pre-mRNAs. Deletion of fission yeast pab2, the homolog of mammalian PABPN1, results in transcripts with markedly longer poly(A) tails, but the nature of the hyperadenylated transcripts and the mechanism that leads to RNA hyperadenylation remain unclear. Here we report that Pab2 functions in the synthesis of noncoding RNAs, contrary to the notion that PABPs function exclusively on protein-coding mRNAs. Accordingly, the absence of Pab2 leads to the accumulation of polyadenylated small nucleolar RNAs (snoRNAs). Our findings suggest that Pab2 promotes poly(A) tail trimming from pre-snoRNAs by recruiting the nuclear exosome. This work unveils a function for the nuclear PABP in snoRNA synthesis and provides insights into exosome recruitment to polyadenylated RNAs.
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Affiliation(s)
- Jean-François Lemay
- RNA Group, Department of Biochemistry, Université de Sherbrooke, Sherbrooke, QC JIH 5N4, Canada
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Hernández G, Altmann M, Lasko P. Origins and evolution of the mechanisms regulating translation initiation in eukaryotes. Trends Biochem Sci 2010; 35:63-73. [DOI: 10.1016/j.tibs.2009.10.009] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2009] [Revised: 10/27/2009] [Accepted: 10/28/2009] [Indexed: 02/08/2023]
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Zhao R, Bin W, Diao Y, Yang J, Liu T, Peng J, Jin Q. Global transcriptional profiles of Trichophyton rubrum in response to Flucytosine. ACTA ACUST UNITED AC 2009; 52:1173-85. [DOI: 10.1007/s11427-009-0153-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2009] [Accepted: 06/22/2009] [Indexed: 11/28/2022]
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19
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Kühn U, Gündel M, Knoth A, Kerwitz Y, Rüdel S, Wahle E. Poly(A) tail length is controlled by the nuclear poly(A)-binding protein regulating the interaction between poly(A) polymerase and the cleavage and polyadenylation specificity factor. J Biol Chem 2009; 284:22803-14. [PMID: 19509282 DOI: 10.1074/jbc.m109.018226] [Citation(s) in RCA: 129] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Poly(A) tails of mRNAs are synthesized in the cell nucleus with a defined length, approximately 250 nucleotides in mammalian cells. The same type of length control is seen in an in vitro polyadenylation system reconstituted from three proteins: poly(A) polymerase, cleavage and polyadenylation specificity factor (CPSF), and the nuclear poly(A)-binding protein (PABPN1). CPSF, binding the polyadenylation signal AAUAAA, and PABPN1, binding the growing poly(A) tail, cooperatively stimulate poly(A) polymerase such that a complete poly(A) tail is synthesized in one processive event, which terminates at a length of approximately 250 nucleotides. We report that PABPN1 is required to restrict CPSF binding to the AAUAAA sequence and to permit the stimulation of poly(A) polymerase by AAUAAA-bound CPSF to be maintained throughout the elongation reaction. The stimulation by CPSF is disrupted when the poly(A) tail has reached a length of approximately 250 nucleotides, and this terminates processive elongation. PABPN1 measures the length of the tail and is responsible for disrupting the CPSF-poly(A) polymerase interaction.
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Affiliation(s)
- Uwe Kühn
- Institute of Biochemistry and Biotechnology, Martin-Luther-University Halle-Wittenberg, Kurt-Mothes-Strasse 3, 06120 Halle, Germany
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Eldad N, Yosefzon Y, Arava Y. Identification and characterization of extensive intra-molecular associations between 3'-UTRs and their ORFs. Nucleic Acids Res 2008; 36:6728-38. [PMID: 18948291 PMCID: PMC2588509 DOI: 10.1093/nar/gkn754] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
During eukaryotic translation, mRNAs may form intra-molecular interactions between distant domains. The 5′-cap and the polyA tail were shown to interact through their associated proteins, and this can induce physical compaction of the mRNA in vitro. However, the stability of this intra-molecular association in translating mRNAs and whether additional contacts exist in vivo are largely unknown. To explore this, we applied a novel approach in which several endogenous polysomal mRNAs from Saccharomyces cerevisiae were cleaved near their stop codon and the resulting 3′-UTR fragments were tested either for co-sedimentation or co-immunoprecipitation (co-IP) with their ORFs. In all cases a significant fraction of the 3′-UTR fragments sedimented similarly to their ORF-containing fragments, yet the extent of co-sedimentation differed between mRNAs. Similar observations were obtained by a co-IP assay. Interestingly, various treatments that are expected to interfere with the cap to polyA interactions had no effect on the co-sedimentation pattern. Moreover, the 3′-UTR appeared to co-sediment with different regions from within the ORF. Taken together, these results indicate extensive physical associations between 3′-UTRs and their ORFs that vary between genes. This implies that polyribosomal mRNAs are in a compact configuration in vivo.
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Affiliation(s)
- Naama Eldad
- Department of Biology, Technion-Israel Institute of Technology, Haifa, Israel
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Viphakone N, Voisinet-Hakil F, Minvielle-Sebastia L. Molecular dissection of mRNA poly(A) tail length control in yeast. Nucleic Acids Res 2008; 36:2418-33. [PMID: 18304944 PMCID: PMC2367721 DOI: 10.1093/nar/gkn080] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
In eukaryotic cells, newly synthesized mRNAs acquire a poly(A) tail that plays several fundamental roles in export, translation and mRNA decay. In mammals, PABPN1 controls the processivity of polyadenylation and the length of poly(A) tails during de novo synthesis. This regulation is less well-detailed in yeast. We have recently demonstrated that Nab2p is necessary and sufficient for the regulation of polyadenylation and that the Pab1p/PAN complex may act at a later stage in mRNA metabolism. Here, we show that the presence of both Pab1p and Nab2p in reconstituted pre-mRNA 3′-end processing reactions has no stimulating nor inhibitory effect on poly(A) tail regulation. Importantly, the poly(A)-binding proteins are essential to protect the mature mRNA from being subjected to a second round of processing. We have determined which domains of Nab2p are important to control polyadenylation and found that the RGG-box work in conjunction with the two last essential CCCH-type zinc finger domains. Finally, we have tried to delineate the mechanism by which Nab2p performs its regulation function during polyadenylation: it likely forms a complex with poly(A) tails different from a simple linear deposit of proteins as it has been observed with Pab1p.
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Affiliation(s)
- Nicolas Viphakone
- Université Victor Segalen Bordeaux 2, CNRS, Institut de Biochimie et Génétique Cellulaires, Bordeaux, France
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De Gaudenzi J, Frasch AC, Clayton C. RNA-binding domain proteins in Kinetoplastids: a comparative analysis. EUKARYOTIC CELL 2006; 4:2106-14. [PMID: 16339728 PMCID: PMC1317496 DOI: 10.1128/ec.4.12.2106-2114.2005] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
RNA-binding proteins are important in many aspects of RNA processing, function, and destruction. One class of such proteins contains the RNA recognition motif (RRM), which consists of about 90 amino acid residues, including the canonical RNP1 octapeptide: (K/R)G(F/Y)(G/A)FVX(F/Y). We used a variety of homology searches to classify all of the RRM proteins of the three kinetoplastids Trypanosoma brucei, Trypanosoma cruzi, and Leishmania major. All three organisms have similar sets of RRM-containing protein orthologues, suggesting common posttranscriptional processing and regulatory pathways. Of the 75 RRM proteins identified in T. brucei, only 13 had clear homologues in other eukaryotes, although 8 more could be given putative functional assignments. A comparison with the 18 RRM proteins of the obligate intracellular parasite Encephalitozoon cuniculi revealed just 3 RRM proteins which appear to be conserved at the primary sequence level throughout eukaryotic evolution: poly(A) binding protein, the rRNA-processing protein MRD1, and the nuclear cap binding protein.
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Affiliation(s)
- Javier De Gaudenzi
- Instituto de Investigaciones Biotecnológicas-Instituto Tecnológico de Chascomús, CONICET-UNSAM, Av. Gral Paz 5445, 1650 Buenos Aires, Argentina
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23
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Gavin AC, Aloy P, Grandi P, Krause R, Boesche M, Marzioch M, Rau C, Jensen LJ, Bastuck S, Dümpelfeld B, Edelmann A, Heurtier MA, Hoffman V, Hoefert C, Klein K, Hudak M, Michon AM, Schelder M, Schirle M, Remor M, Rudi T, Hooper S, Bauer A, Bouwmeester T, Casari G, Drewes G, Neubauer G, Rick JM, Kuster B, Bork P, Russell RB, Superti-Furga G. Proteome survey reveals modularity of the yeast cell machinery. Nature 2006; 440:631-6. [PMID: 16429126 DOI: 10.1038/nature04532] [Citation(s) in RCA: 1826] [Impact Index Per Article: 101.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2005] [Accepted: 12/15/2005] [Indexed: 11/08/2022]
Abstract
Protein complexes are key molecular entities that integrate multiple gene products to perform cellular functions. Here we report the first genome-wide screen for complexes in an organism, budding yeast, using affinity purification and mass spectrometry. Through systematic tagging of open reading frames (ORFs), the majority of complexes were purified several times, suggesting screen saturation. The richness of the data set enabled a de novo characterization of the composition and organization of the cellular machinery. The ensemble of cellular proteins partitions into 491 complexes, of which 257 are novel, that differentially combine with additional attachment proteins or protein modules to enable a diversification of potential functions. Support for this modular organization of the proteome comes from integration with available data on expression, localization, function, evolutionary conservation, protein structure and binary interactions. This study provides the largest collection of physically determined eukaryotic cellular machines so far and a platform for biological data integration and modelling.
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Dunn EF, Hammell CM, Hodge CA, Cole CN. Yeast poly(A)-binding protein, Pab1, and PAN, a poly(A) nuclease complex recruited by Pab1, connect mRNA biogenesis to export. Genes Dev 2005; 19:90-103. [PMID: 15630021 PMCID: PMC540228 DOI: 10.1101/gad.1267005] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2004] [Accepted: 11/02/2004] [Indexed: 11/25/2022]
Abstract
In eukaryotic cells, pre-mRNAs undergo extensive processing in the nucleus prior to export. Processing is subject to a quality-control mechanism that retains improperly processed transcripts at or near sites of transcription. A poly(A) tail added by the normal 3'-processing machinery is necessary but not sufficient for export. Retention depends on the exosome. In this study, we identify the poly(A)-binding protein, Pab1, and the poly(A) nuclease, PAN, as important factors that couple 3' processing to export. Pab1 contains a nonessential leucine-rich nuclear export signal and shuttles between the nucleus and the cytoplasm. It can exit the nucleus either as cargo of exportin 1 or bound to mRNA. Pab1 is essential but several bypass suppressors have been identified. Deletion of PAB1 from these bypass suppressor strains results in exosome-dependent retention at sites of transcription. Retention is also seen in cells lacking PAN, which Pab1 is thought to recruit and which may be responsible for the final step of mRNA biogenesis, trimming of the poly(A) tail to the length found on newly exported mRNAs. The studies presented here suggest that proper loading of Pab1 onto mRNAs and final trimming of the tail allows release from transcription sites and couples pre-mRNA processing to export.
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Affiliation(s)
- Ewan F Dunn
- Department of Biochemistry, the Norris Cotton Cancer Center, Dartmouth Medical School, Hanover, New Hampshire 03755, USA
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25
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Kühn U, Wahle E. Structure and function of poly(A) binding proteins. ACTA ACUST UNITED AC 2004; 1678:67-84. [PMID: 15157733 DOI: 10.1016/j.bbaexp.2004.03.008] [Citation(s) in RCA: 242] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2004] [Revised: 03/30/2004] [Accepted: 03/31/2004] [Indexed: 01/01/2023]
Abstract
Poly (A) tails are found at the 3' ends of almost all eukaryotic mRNAs. They are bound by two different poly (A) binding proteins, PABPC in the cytoplasm and PABPN1 in the nucleus. PABPC functions in the initiation of translation and in the regulation of mRNA decay. In both functions, an interaction with the m7G cap at the 5' end of the message plays an important role. PABPN1 is involved in the synthesis of poly (A) tails, increasing the processivity of poly (A) polymerase and contributing to defining the length of a newly synthesized poly (A) tail.
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Affiliation(s)
- Uwe Kühn
- Institut für Biochemie, Martin-Luther-Universität Halle-Wittenberg, Kurt-Mothes-Stasse. 3, D-06120 Halle, Germany
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Baron-Benhamou J, Fortes P, Inada T, Preiss T, Hentze MW. The interaction of the cap-binding complex (CBC) with eIF4G is dispensable for translation in yeast. RNA (NEW YORK, N.Y.) 2003; 9:654-62. [PMID: 12756324 PMCID: PMC1370433 DOI: 10.1261/rna.5100903] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/17/2003] [Accepted: 02/20/2003] [Indexed: 05/19/2023]
Abstract
In eukaryotes, the m(7)GpppN cap structure is added to all nascent RNA polymerase II transcripts, and serves important functions at multiple steps of RNA metabolism. The predominantly nuclear cap-binding complex (CBC) binds to the cap during RNA synthesis. The predominantly cytoplasmic eukaryotic initiation factor 4F (eIF4F) is thought to replace CBC after export of mature mRNA to the cytoplasm, and mediates the bulk of cellular translation. Yeast as well as mammalian CBC interacts in vitro with eIF4G, a subunit of eIF4F. In this work, we investigate a potential role of this interaction during translation in yeast. We identify a mutation (DR548/9AA) in Tif4631p, one of two isoforms of yeast eIF4G, that abolishes its binding to CBC. Cells expressing this mutant protein as the sole source of eIF4G grow at wild-type rates, and bulk cellular translation, as assessed by metabolic labeling and polysome profile analysis, is unchanged. Importantly, we find that the DR548/9AA mutation neither diminishes nor delays the translation of newly induced reporter mRNA. Finally, microarray analysis reveals marked transcriptome alterations in CBC subunit deletion strains, whereas eIF4G point mutants have essentially a wild-type transcriptome composition. Collectively, these data suggest that in yeast, the phenotypic consequences of CBC deletions are separable from its interaction with eIF4G, and that the CBC-eIF4G interaction is dispensable for a potential "pioneering round" of translation in yeast.
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Affiliation(s)
- Julie Baron-Benhamou
- Gene Expression Programme, European Molecular Biology Laboratory, 69117 Heidelberg, Germany
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Kühn U, Nemeth A, Meyer S, Wahle E. The RNA binding domains of the nuclear poly(A)-binding protein. J Biol Chem 2003; 278:16916-25. [PMID: 12637556 DOI: 10.1074/jbc.m209886200] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The nuclear poly(A)-binding protein (PABPN1) is involved in the synthesis of the mRNA poly(A) tails in most eukaryotes. We report that the protein contains two RNA binding domains, a ribonucleoprotein-type RNA binding domain (RNP domain) located approximately in the middle of the protein sequence and an arginine-rich C-terminal domain. The C-terminal domain also promotes self-association of PABPN1 and moderately cooperative binding to RNA. Whereas the isolated RNP domain binds specifically to poly(A), the isolated C-terminal domain binds non-specifically to RNA and other polyanions. Despite this nonspecific RNA binding by the C-terminal domain, selection experiments show that adenosine residues throughout the entire minimal binding site of approximately 11 nucleotides are recognized specifically. UV-induced cross-links with oligo(A) carrying photoactivatable nucleotides at different positions all map to the RNP domain, suggesting that most or all of the base-specific contacts are made by the RNP domain, whereas the C-terminal domain may contribute nonspecific contacts, conceivably to the same nucleotides. Asymmetric dimethylation of 13 arginine residues in the C-terminal domain has no detectable influence on the interaction of the protein with RNA. The N-terminal domain of PABPN1 is not required for RNA binding but is essential for the stimulation of poly(A) polymerase.
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Affiliation(s)
- Uwe Kühn
- Institut für Biochemie, Martin-Luther-Universität Halle, 06099 Halle, Germany
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Asano K, Shalev A, Phan L, Nielsen K, Clayton J, Valášek L, Donahue TF, Hinnebusch AG. Multiple roles for the C-terminal domain of eIF5 in translation initiation complex assembly and GTPase activation. EMBO J 2001; 20:2326-37. [PMID: 11331597 PMCID: PMC125443 DOI: 10.1093/emboj/20.9.2326] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
eIF5 stimulates the GTPase activity of eIF2 bound to Met-tRNA(i)(Met), and its C-terminal domain (eIF5-CTD) bridges interaction between eIF2 and eIF3/eIF1 in a multifactor complex containing Met-tRNA(i)(Met). The tif5-7A mutation in eIF5-CTD, which destabilizes the multifactor complex in vivo, reduced the binding of Met-tRNA(i)(Met) and mRNA to 40S subunits in vitro. Interestingly, eIF5-CTD bound simultaneously to the eIF4G subunit of the cap-binding complex and the NIP1 subunit of eIF3. These interactions may enhance association of eIF4G with eIF3 to promote mRNA binding to the ribosome. In vivo, tif5-7A eliminated eIF5 as a stable component of the pre-initiation complex and led to accumulation of 48S complexes containing eIF2; thus, conversion of 48S to 80S complexes is the rate-limiting defect in this mutant. We propose that eIF5-CTD stimulates binding of Met-tRNA(i)(Met) and mRNA to 40S subunits through interactions with eIF2, eIF3 and eIF4G; however, its most important function is to anchor eIF5 to other components of the 48S complex in a manner required to couple GTP hydrolysis to AUG recognition during the scanning phase of initiation.
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Affiliation(s)
- Katsura Asano
- Laboratory of Gene Regulation and Development, National Institute of Child Health and Human Development, NIH, Bethesda, MD 20892 and
Department of Biology, Indiana University, Bloomington, IN 47405, USA Present address: Division of Biology, Kansas State University, Manhattan, KS 66506, USA Corresponding author e-mail:
| | | | | | | | | | | | - Thomas F. Donahue
- Laboratory of Gene Regulation and Development, National Institute of Child Health and Human Development, NIH, Bethesda, MD 20892 and
Department of Biology, Indiana University, Bloomington, IN 47405, USA Present address: Division of Biology, Kansas State University, Manhattan, KS 66506, USA Corresponding author e-mail:
| | - Alan G. Hinnebusch
- Laboratory of Gene Regulation and Development, National Institute of Child Health and Human Development, NIH, Bethesda, MD 20892 and
Department of Biology, Indiana University, Bloomington, IN 47405, USA Present address: Division of Biology, Kansas State University, Manhattan, KS 66506, USA Corresponding author e-mail:
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