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Ntini E, Budach S, Vang Ørom UA, Marsico A. Genome-wide measurement of RNA dissociation from chromatin classifies transcripts by their dynamics and reveals rapid dissociation of enhancer lncRNAs. Cell Syst 2023; 14:906-922.e6. [PMID: 37857083 DOI: 10.1016/j.cels.2023.09.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2022] [Revised: 05/24/2023] [Accepted: 09/20/2023] [Indexed: 10/21/2023]
Abstract
Long non-coding RNAs (lncRNAs) are involved in gene expression regulation in cis. Although enriched in the cell chromatin fraction, to what degree this defines their regulatory potential remains unclear. Furthermore, the factors underlying lncRNA chromatin tethering, as well as the molecular basis of efficient lncRNA chromatin dissociation and its impact on enhancer activity and target gene expression, remain to be resolved. Here, we developed chrTT-seq, which combines the pulse-chase metabolic labeling of nascent RNA with chromatin fractionation and transient transcriptome sequencing to follow nascent RNA transcripts from their transcription on chromatin to release and allows the quantification of dissociation dynamics. By incorporating genomic, transcriptomic, and epigenetic metrics, as well as RNA-binding protein propensities, in machine learning models, we identify features that define transcript groups of different chromatin dissociation dynamics. Notably, lncRNAs transcribed from enhancers display reduced chromatin retention, suggesting that, in addition to splicing, their chromatin dissociation may shape enhancer activity.
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Affiliation(s)
- Evgenia Ntini
- Max-Planck Institute for Molecular Genetics, 14195 Berlin, Germany; Freie Universität Berlin, 14195 Berlin, Germany; Institute of Molecular Biology and Biotechnology, IMBB-FORTH, 70013 Heraklio, Greece.
| | - Stefan Budach
- Max-Planck Institute for Molecular Genetics, 14195 Berlin, Germany; Freie Universität Berlin, 14195 Berlin, Germany
| | - Ulf A Vang Ørom
- Aarhus University, Department of Molecular Biology and Genetics, 8000 Aarhus, Denmark
| | - Annalisa Marsico
- Max-Planck Institute for Molecular Genetics, 14195 Berlin, Germany; Freie Universität Berlin, 14195 Berlin, Germany; Computational Health Center, Helmholtz Center Munich, Munich, Germany.
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2
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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: 5] [Impact Index Per Article: 5.0] [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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3
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Slight Variations in the Sequence Downstream of the Polyadenylation Signal Significantly Increase Transgene Expression in HEK293T and CHO Cells. Int J Mol Sci 2022; 23:ijms232415485. [PMID: 36555130 PMCID: PMC9779314 DOI: 10.3390/ijms232415485] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2022] [Revised: 11/28/2022] [Accepted: 12/01/2022] [Indexed: 12/13/2022] Open
Abstract
Compared to transcription initiation, much less is known about transcription termination. In particular, large-scale mutagenesis studies have, so far, primarily concentrated on promoter and enhancer, but not terminator sequences. Here, we used a massively parallel reporter assay (MPRA) to systematically analyze the influence of short (8 bp) sequence variants (mutations) located downstream of the polyadenylation signal (PAS) on the steady-state mRNA level of the upstream gene, employing an eGFP reporter and human HEK293T cells as a model system. In total, we evaluated 227,755 mutations located at different overlapping positions within +17..+56 bp downstream of the PAS for their ability to regulate the reporter gene expression. We found that the positions +17..+44 bp downstream of the PAS are more essential for gene upregulation than those located more distal to the PAS, and that the mutation sequences ensuring high levels of eGFP mRNA expression are extremely T-rich. Next, we validated the positive effect of a couple of mutations identified in the MPRA screening on the eGFP and luciferase protein expression. The most promising mutation increased the expression of the reporter proteins 13-fold and sevenfold on average in HEK293T and CHO cells, respectively. Overall, these findings might be useful for further improving the efficiency of production of therapeutic products, e.g., recombinant antibodies.
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4
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Nicholson-Shaw AL, Kofman ER, Yeo GW, Pasquinelli A. Nuclear and cytoplasmic poly(A) binding proteins (PABPs) favor distinct transcripts and isoforms. Nucleic Acids Res 2022; 50:4685-4702. [PMID: 35438785 PMCID: PMC9071453 DOI: 10.1093/nar/gkac263] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2022] [Revised: 03/23/2022] [Accepted: 04/04/2022] [Indexed: 11/14/2022] Open
Abstract
The poly(A)-tail appended to the 3'-end of most eukaryotic transcripts plays a key role in their stability, nuclear transport, and translation. These roles are largely mediated by Poly(A) Binding Proteins (PABPs) that coat poly(A)-tails and interact with various proteins involved in the biogenesis and function of RNA. While it is well-established that the nuclear PABP (PABPN) binds newly synthesized poly(A)-tails and is replaced by the cytoplasmic PABP (PABPC) on transcripts exported to the cytoplasm, the distribution of transcripts for different genes or isoforms of the same gene on these PABPs has not been investigated on a genome-wide scale. Here, we analyzed the identity, splicing status, poly(A)-tail size, and translation status of RNAs co-immunoprecipitated with endogenous PABPN or PABPC in human cells. At steady state, many protein-coding and non-coding RNAs exhibit strong bias for association with PABPN or PABPC. While PABPN-enriched transcripts more often were incompletely spliced and harbored longer poly(A)-tails and PABPC-enriched RNAs had longer half-lives and higher translation efficiency, there are curious outliers. Overall, our study reveals the landscape of RNAs bound by PABPN and PABPC, providing new details that support and advance the current understanding of the roles these proteins play in poly(A)-tail synthesis, maintenance, and function.
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Affiliation(s)
| | - Eric R Kofman
- Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA 92093, USA
- UCSD Stem Cell Program, Sanford Consortium for Regenerative Medicine, La Jolla, CA 92037, USA
- Institute for Genomic Medicine, University of California San Diego, La Jolla, CA 92093, USA
| | - Gene W Yeo
- Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA 92093, USA
- UCSD Stem Cell Program, Sanford Consortium for Regenerative Medicine, La Jolla, CA 92037, USA
- Institute for Genomic Medicine, University of California San Diego, La Jolla, CA 92093, USA
| | - Amy E Pasquinelli
- Division of Biology, University of California, San Diego, La Jolla, CA 92093, USA
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5
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Lu YY, Krebber H. Nuclear mRNA Quality Control and Cytoplasmic NMD Are Linked by the Guard Proteins Gbp2 and Hrb1. Int J Mol Sci 2021; 22:ijms222011275. [PMID: 34681934 PMCID: PMC8541090 DOI: 10.3390/ijms222011275] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2021] [Revised: 10/13/2021] [Accepted: 10/17/2021] [Indexed: 12/23/2022] Open
Abstract
Pre-mRNA splicing is critical for cells, as defects in this process can lead to altered open reading frames and defective proteins, potentially causing neurodegenerative diseases and cancer. Introns are removed in the nucleus and splicing is documented by the addition of exon-junction-complexes (EJCs) at exon-exon boundaries. This “memory” of splicing events is important for the ribosome, which translates the RNAs in the cytoplasm. In case a stop codon was detected before an EJC, translation is blocked and the RNA is eliminated by the nonsense-mediated decay (NMD). In the model organism Saccharomyces cerevisiae, two guard proteins, Gbp2 and Hrb1, have been identified as nuclear quality control factors for splicing. In their absence, intron-containing mRNAs leak into the cytoplasm. Their presence retains transcripts until the process is completed and they release the mRNAs by recruitment of the export factor Mex67. On transcripts that experience splicing problems, these guard proteins recruit the nuclear RNA degradation machinery. Interestingly, they continue their quality control function on exported transcripts. They support NMD by inhibiting translation and recruiting the cytoplasmic degradation factors. In this way, they link the nuclear and cytoplasmic quality control systems. These discoveries are also intriguing for humans, as homologues of these guard proteins are present also in multicellular organisms. Here, we provide an overview of the quality control mechanisms of pre-mRNA splicing, and present Gbp2 and Hrb1, as well as their human counterparts, as important players in these pathways.
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6
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Mora Gallardo C, Sánchez de Diego A, Martínez-A C, van Wely KHM. Interplay between splicing and transcriptional pausing exerts genome-wide control over alternative polyadenylation. Transcription 2021; 12:55-71. [PMID: 34365909 PMCID: PMC8555548 DOI: 10.1080/21541264.2021.1959244] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Recent studies have identified multiple polyadenylation sites in nearly all mammalian genes. Although these are interpreted as evidence for alternative polyadenylation, our knowledge of the underlying mechanisms is still limited. Most studies only consider the immediate surroundings of gene ends, even though in vitro experiments have uncovered the involvement of external factors such as splicing. Whereas in vivo splicing manipulation was impracticable until recently, we now used mutants in the Death Inducer Obliterator (DIDO) gene to study their impact on 3ʹ end processing. We observe multiple rounds of readthrough and gene fusions, suggesting that no arbitration between polyadenylation sites occurs. Instead, a window of opportunity seems to control end processing. Through the identification of T-rich sequence motifs, our data indicate that splicing and transcriptional pausing interact to regulate alternative polyadenylation. We propose that 3ʹ splice site activation comprises a variable timer, which determines how long transcription proceeds before polyadenylation signals are recognized. Thus, the role of core polyadenylation signals could be more passive than commonly believed. Our results provide new insights into the mechanisms of alternative polyadenylation and expand the catalog of related aberrations. Abbreviations APA: alternative polyadenylation; bp: basepair; MEF: mouse embryonic fibroblasts; PA: polyadenylation; PAS: polyadenylation site; Pol II: (RNA) polymerase II ; RT-PCR:reverse-transcriptase PCR; SF:splicing factor; SFPQ:splicing factor rich in proline and glutamine; SS:splice site; TRSM:Thymidine rich sequence motif; UTR:untranslated terminal region
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Affiliation(s)
- Carmen Mora Gallardo
- Department of Immunology and Oncology Centro Nacional De Biotecnología (CNB)/, CSIC Darwin 3, Campus UAM Cantoblanco, Madrid, Spain
| | - Ainhoa Sánchez de Diego
- Department of Immunology and Oncology Centro Nacional De Biotecnología (CNB)/, CSIC Darwin 3, Campus UAM Cantoblanco, Madrid, Spain
| | - Carlos Martínez-A
- Department of Immunology and Oncology Centro Nacional De Biotecnología (CNB)/, CSIC Darwin 3, Campus UAM Cantoblanco, Madrid, Spain
| | - Karel H M van Wely
- Department of Immunology and Oncology Centro Nacional De Biotecnología (CNB)/, CSIC Darwin 3, Campus UAM Cantoblanco, Madrid, Spain
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7
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Long non-coding RNAs and splicing. Essays Biochem 2021; 65:723-729. [PMID: 33835135 DOI: 10.1042/ebc20200087] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2020] [Revised: 02/05/2021] [Accepted: 03/15/2021] [Indexed: 12/25/2022]
Abstract
In this review I focus on the role of splicing in long non-coding RNA (lncRNA) life. First, I summarize differences between the splicing efficiency of protein-coding genes and lncRNAs and discuss why non-coding RNAs are spliced less efficiently. In the second half of the review, I speculate why splice sites are the most conserved sequences in lncRNAs and what additional roles could splicing play in lncRNA metabolism. I discuss the hypothesis that the splicing machinery can, besides its dominant role in intron removal and exon joining, protect cells from undesired transcripts.
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8
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Ntini E, Marsico A. Functional impacts of non-coding RNA processing on enhancer activity and target gene expression. J Mol Cell Biol 2020; 11:868-879. [PMID: 31169884 PMCID: PMC6884709 DOI: 10.1093/jmcb/mjz047] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2019] [Revised: 04/03/2019] [Accepted: 04/04/2019] [Indexed: 01/06/2023] Open
Abstract
Tight regulation of gene expression is orchestrated by enhancers. Through recent research advancements, it is becoming clear that enhancers are not solely distal regulatory elements harboring transcription factor binding sites and decorated with specific histone marks, but they rather display signatures of active transcription, showing distinct degrees of transcription unit organization. Thereby, a substantial fraction of enhancers give rise to different species of non-coding RNA transcripts with an unprecedented range of potential functions. In this review, we bring together data from recent studies indicating that non-coding RNA transcription from active enhancers, as well as enhancer-produced long non-coding RNA transcripts, may modulate or define the functional regulatory potential of the cognate enhancer. In addition, we summarize supporting evidence that RNA processing of the enhancer-associated long non-coding RNA transcripts may constitute an additional layer of regulation of enhancer activity, which contributes to the control and final outcome of enhancer-targeted gene expression.
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Affiliation(s)
- Evgenia Ntini
- Max Planck Institute for Molecular Genetics, Berlin, Germany.,Free University Berlin, Berlin, Germany
| | - Annalisa Marsico
- Max Planck Institute for Molecular Genetics, Berlin, Germany.,Free University Berlin, Berlin, Germany.,Institute of Computational Biology, Helmholtz Zentrum München, München, Germany
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9
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10
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Ntini E, Louloupi A, Liz J, Muino JM, Marsico A, Ørom UAV. Long ncRNA A-ROD activates its target gene DKK1 at its release from chromatin. Nat Commun 2018; 9:1636. [PMID: 29691407 PMCID: PMC5915440 DOI: 10.1038/s41467-018-04100-3] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2017] [Accepted: 04/04/2018] [Indexed: 12/20/2022] Open
Abstract
Long ncRNAs are often enriched in the nucleus and at chromatin, but whether their dissociation from chromatin is important for their role in transcription regulation is unclear. Here, we group long ncRNAs using epigenetic marks, expression and strength of chromosomal interactions; we find that long ncRNAs transcribed from loci engaged in strong long-range chromosomal interactions are less abundant at chromatin, suggesting the release from chromatin as a crucial functional aspect of long ncRNAs in transcription regulation of their target genes. To gain mechanistic insight into this, we functionally validate the long ncRNA A-ROD, which enhances DKK1 transcription via its nascent spliced released form. Our data provide evidence that the regulatory interaction requires dissociation of A-ROD from chromatin, with target specificity ensured within the pre-established chromosomal proximity. We propose that the post-transcriptional release of a subset of long ncRNAs from the chromatin-associated template plays an important role in their function as transcription regulators.
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Affiliation(s)
- Evgenia Ntini
- Max Planck Institute for Molecular Genetics, 14195, Berlin, Germany.
| | - Annita Louloupi
- Max Planck Institute for Molecular Genetics, 14195, Berlin, Germany.,Free University Berlin, 14195, Berlin, Germany
| | - Julia Liz
- Max Planck Institute for Molecular Genetics, 14195, Berlin, Germany
| | | | - Annalisa Marsico
- Max Planck Institute for Molecular Genetics, 14195, Berlin, Germany.,Free University Berlin, 14195, Berlin, Germany
| | - Ulf Andersson Vang Ørom
- Max Planck Institute for Molecular Genetics, 14195, Berlin, Germany. .,Institute for Molecular Biology and Genetics, Aarhus University, 8000, Aarhus, Denmark.
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11
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Björk P, Wieslander L. Integration of mRNP formation and export. Cell Mol Life Sci 2017; 74:2875-2897. [PMID: 28314893 PMCID: PMC5501912 DOI: 10.1007/s00018-017-2503-3] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Revised: 03/06/2017] [Accepted: 03/07/2017] [Indexed: 12/13/2022]
Abstract
Expression of protein-coding genes in eukaryotes relies on the coordinated action of many sophisticated molecular machineries. Transcription produces precursor mRNAs (pre-mRNAs) and the active gene provides an environment in which the pre-mRNAs are processed, folded, and assembled into RNA–protein (RNP) complexes. The dynamic pre-mRNPs incorporate the growing transcript, proteins, and the processing machineries, as well as the specific protein marks left after processing that are essential for export and the cytoplasmic fate of the mRNPs. After release from the gene, the mRNPs move by diffusion within the interchromatin compartment, making up pools of mRNPs. Here, splicing and polyadenylation can be completed and the mRNPs recruit the major export receptor NXF1. Export competent mRNPs interact with the nuclear pore complex, leading to export, concomitant with compositional and conformational changes of the mRNPs. We summarize the integrated nuclear processes involved in the formation and export of mRNPs.
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Affiliation(s)
- Petra Björk
- Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, 106 91 Stockholm, Sweden
| | - Lars Wieslander
- Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, 106 91 Stockholm, Sweden
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12
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Leigh-Brown S, Goncalves A, Thybert D, Stefflova K, Watt S, Flicek P, Brazma A, Marioni JC, Odom DT. Regulatory Divergence of Transcript Isoforms in a Mammalian Model System. PLoS One 2015; 10:e0137367. [PMID: 26339903 PMCID: PMC4560434 DOI: 10.1371/journal.pone.0137367] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2015] [Accepted: 08/15/2015] [Indexed: 11/24/2022] Open
Abstract
Phenotypic differences between species are driven by changes in gene expression and, by extension, by modifications in the regulation of the transcriptome. Investigation of mammalian transcriptome divergence has been restricted to analysis of bulk gene expression levels and gene-internal splicing. Using allele-specific expression analysis in inter-strain hybrids of Mus musculus, we determined the contribution of multiple cellular regulatory systems to transcriptome divergence, including: alternative promoter usage, transcription start site selection, cassette exon usage, alternative last exon usage, and alternative polyadenylation site choice. Between mouse strains, a fifth of genes have variations in isoform usage that contribute to transcriptomic changes, half of which alter encoded amino acid sequence. Virtually all divergence in isoform usage altered the post-transcriptional regulatory instructions in gene UTRs. Furthermore, most genes with isoform differences between strains contain changes originating from multiple regulatory systems. This result indicates widespread cross-talk and coordination exists among different regulatory systems. Overall, isoform usage diverges in parallel with and independently to gene expression evolution, and the cis and trans regulatory contribution to each differs significantly.
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Affiliation(s)
- Sarah Leigh-Brown
- University of Cambridge, Cancer Research UK - Cambridge Institute, Li Ka Shing Centre, Cambridge, United Kingdom
| | - Angela Goncalves
- European Molecular Biology Laboratory, European Bioinformatics Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, United Kingdom
- Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, United Kingdom
| | - David Thybert
- European Molecular Biology Laboratory, European Bioinformatics Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, United Kingdom
| | - Klara Stefflova
- California Institute of Technology, Division of Biology, Pasadena, California, United States of America
| | - Stephen Watt
- Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, United Kingdom
| | - Paul Flicek
- European Molecular Biology Laboratory, European Bioinformatics Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, United Kingdom
| | - Alvis Brazma
- European Molecular Biology Laboratory, European Bioinformatics Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, United Kingdom
| | - John C. Marioni
- European Molecular Biology Laboratory, European Bioinformatics Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, United Kingdom
| | - Duncan T. Odom
- University of Cambridge, Cancer Research UK - Cambridge Institute, Li Ka Shing Centre, Cambridge, United Kingdom
- Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, United Kingdom
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13
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Morris DP, Lei B, Longo LD, Bomsztyk K, Schwinn DA, Michelotti GA. Temporal Dissection of Rate Limiting Transcriptional Events Using Pol II ChIP and RNA Analysis of Adrenergic Stress Gene Activation. PLoS One 2015; 10:e0134442. [PMID: 26244980 PMCID: PMC4526373 DOI: 10.1371/journal.pone.0134442] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2014] [Accepted: 07/10/2015] [Indexed: 12/13/2022] Open
Abstract
In mammals, increasing evidence supports mechanisms of co-transcriptional gene regulation and the generality of genetic control subsequent to RNA polymerase II (Pol II) recruitment. In this report, we use Pol II Chromatin Immunoprecipitation to investigate relationships between the mechanistic events controlling immediate early gene (IEG) activation following stimulation of the α1a-Adrenergic Receptor expressed in rat-1 fibroblasts. We validate our Pol II ChIP assay by comparison to major transcriptional events assessable by microarray and PCR analysis of precursor and mature mRNA. Temporal analysis of Pol II density suggests that reduced proximal pausing often enhances gene expression and was essential for Nr4a3 expression. Nevertheless, for Nr4a3 and several other genes, proximal pausing delayed the time required for initiation of productive elongation, consistent with a role in ensuring transcriptional fidelity. Arrival of Pol II at the 3’ cleavage site usually correlated with increased polyadenylated mRNA; however, for Nfil3 and probably Gprc5a expression was delayed and accompanied by apparent pre-mRNA degradation. Intragenic pausing not associated with polyadenylation was also found to regulate and delay Gprc5a expression. Temporal analysis of Nr4a3, Dusp5 and Nfil3 shows that transcription of native IEG genes can proceed at velocities of 3.5 to 4 kilobases/min immediately after activation. Of note, all of the genes studied here also used increased Pol II recruitment as an important regulator of expression. Nevertheless, the generality of co-transcriptional regulation during IEG activation suggests temporal and integrated analysis will often be necessary to distinguish causative from potential rate limiting mechanisms.
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Affiliation(s)
- Daniel P. Morris
- Center for Perinatal Biology, Loma Linda University, Loma Linda, California, United States of America
- * E-mail:
| | - Beilei Lei
- Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina, United States of America
| | - Lawrence D. Longo
- Center for Perinatal Biology, Loma Linda University, Loma Linda, California, United States of America
| | - Karol Bomsztyk
- Department of Medicine, University of Washington, Seattle, Washington, United States of America
| | - Debra A. Schwinn
- Department of Anesthesiology, University of Iowa Carver College of Medicine, Iowa City, Iowa, United States of America
- Department of Pharmacology, University of Iowa Carver College of Medicine, Iowa City, Iowa, United States of America
- Department of Biochemistry, University of Iowa Carver College of Medicine, Iowa City, Iowa, United States of America
| | - Gregory A. Michelotti
- Department of Medicine, Division of Gastroenterology, Duke University Medical Center, Durham, North Carolina, United States of America
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14
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Poly(A) Signal-Dependent Transcription Termination Occurs through a Conformational Change Mechanism that Does Not Require Cleavage at the Poly(A) Site. Mol Cell 2015; 59:437-48. [PMID: 26166703 DOI: 10.1016/j.molcel.2015.06.008] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2014] [Revised: 04/24/2015] [Accepted: 06/03/2015] [Indexed: 12/18/2022]
Abstract
Transcription termination for genes encoding polyadenylated mRNAs requires a functional poly(A) signal (PAS) in the nascent pre-mRNA. Often called PAS-dependent termination, or PADT, it is widely assumed that the PAS requirement reflects an obligatory poly(A) site cleavage requirement for termination. Cleavage is thought to provide entry for a 5'-to-3' exonuclease that targets RNA polymerase II via the nascent transcript-i.e., the torpedo model. To assess the role of cleavage in PADT, we developed a PADT assay using HeLa nuclear extract. Here we examine the basal mechanism of PADT and show that cleavage at the poly(A) site is not required for PADT. Isolated elongation complexes undergo termination in a PAS-dependent manner when incubated in buffer, in the absence of extract, nucleotides, or cleavage at the poly(A) site. Thus, PADT-proficient complexes undergo a conformational change that triggers termination. PADT is inhibited by α-amanitin, which presumably blocks the required conformational change.
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15
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Abstract
The spliceosomal factor TRAP150 is essential for pre-mRNA splicing in vivo and, when overexpressed, it enhances splicing efficiency. In this study, we found that TRAP150 interacted with the cleavage and polyadenylation specificity factor (CPSF) and co-fractionated with CPSF and RNA polymerase II. Moreover, TRAP150 preferentially associated with the U1 small ribonucleoprotein (snRNP). However, our data do not support a role for TRAP150 in alternative 5′ splice site or exon selection or in alternative polyadenylation. Because U1 snRNP participates in premature cleavage and polyadenylation (PCPA), we tested whether TRAP150 is a cofactor in the control of PCPA. Although TRAP150 depletion had no significant effect on PCPA, overexpression of TRAP150 forced activation of a cryptic 3′ splice site, yielding spliced PCPA transcripts. Mechanistic studies showed that TRAP150-activated splicing occurred in composite but not authentic terminal exons, and such an activity was enhanced by debilitation of U1 snRNP or interference with transcription elongation or termination. Together, these results indicate that TRAP150 provides an additional layer of PCPA regulation, through which it may increase the diversity of abortive RNA transcripts under conditions of compromised gene expression.
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Affiliation(s)
- Kuo-Ming Lee
- Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan
| | - Woan-Yuh Tarn
- Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan
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16
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Quality control of mRNP biogenesis: networking at the transcription site. Semin Cell Dev Biol 2014; 32:37-46. [PMID: 24713468 DOI: 10.1016/j.semcdb.2014.03.033] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2014] [Accepted: 03/28/2014] [Indexed: 11/20/2022]
Abstract
Eukaryotic cells carry out quality control (QC) over the processes of RNA biogenesis to inactivate or eliminate defective transcripts, and to avoid their production. In the case of protein-coding transcripts, the quality controls can sense defects in the assembly of mRNA-protein complexes, in the processing of the precursor mRNAs, and in the sequence of open reading frames. Different types of defect are monitored by different specialized mechanisms. Some of them involve dedicated factors whose function is to identify faulty molecules and target them for degradation. Others are the result of a more subtle balance in the kinetics of opposing activities in the mRNA biogenesis pathway. One way or another, all such mechanisms hinder the expression of the defective mRNAs through processes as diverse as rapid degradation, nuclear retention and transcriptional silencing. Three major degradation systems are responsible for the destruction of the defective transcripts: the exosome, the 5'-3' exoribonucleases, and the nonsense-mediated mRNA decay (NMD) machinery. This review summarizes recent findings on the cotranscriptional quality control of mRNA biogenesis, and speculates that a protein-protein interaction network integrates multiple mRNA degradation systems with the transcription machinery.
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17
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Huang H, Chen J, Liu H, Sun X. The nucleosome regulates the usage of polyadenylation sites in the human genome. BMC Genomics 2013; 14:912. [PMID: 24365105 PMCID: PMC3879661 DOI: 10.1186/1471-2164-14-912] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2013] [Accepted: 12/19/2013] [Indexed: 12/13/2022] Open
Abstract
Background It has been reported that 3' end processing is coupled to transcription and nucleosome depletion near the polyadenylation sites in many species. However, the association between nucleosome occupancy and polyadenylation site usage is still unclear. Results By systematic analysis of high-throughput sequencing datasets from the human genome, we found that nucleosome occupancy patterns are different around the polyadenylation sites, and that the patterns associate with both transcription termination and recognition of polyadenylation sites. Upstream of proximal polyadenylation sites, RNA polymerase II accumulated and nucleosomes were better positioned compared with downstream of the sites. Highly used proximal polyadenylation sites had higher upstream nucleosome levels and RNA polymerase II accumulation than lowly used sites. This suggests that nucleosomes positioned upstream of proximal sites function in the recognition of proximal polyadenylation sites and in the preparation for 3' end processing by slowing down transcription speed. Both conserved distal polyadenylation sites and constitutive sites showed stronger nucleosome depletion near polyadenylation sites and had intrinsically better positioned downstream nucleosomes. Finally, there was a higher accumulation of RNA polymerase II downstream of the polyadenylation sites, to guarantee gene transcription termination and recognition of the last polyadenylation sites, if previous sites were missed. Conclusions Our study indicates that nucleosome arrays play different roles in the regulation of the usage of polyadenylation sites and transcription termination of protein-coding genes, and form a dual pausing model of RNA polymerase II in the alternative polyadenylation sites’ region, to ensure effective 3' end processing.
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Affiliation(s)
| | | | | | - Xiao Sun
- State Key Laboratory of Bioelectronics, School of Biological Science and Medical Engineering, Southeast University, Nanjing 210096, China.
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18
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Tikhonov M, Georgiev P, Maksimenko O. Competition within Introns: Splicing Wins over Polyadenylation via a General Mechanism. Acta Naturae 2013; 5:52-61. [PMID: 24455183 PMCID: PMC3890989] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Most eukaryotic messenger RNAs are capped, spliced, and polyadenylated via co-transcriptional processes that are coupled to each other and to the transcription machinery. Coordination of these processes ensures correct RNA maturation and provides for the diversity of the transcribed isoforms. Thus, RNA processing is a chain of events in which the completion of one event is coupled to the initiation of the next one. In this context, the relationship between splicing and polyadenylation is an important aspect of gene regulation. We have found that cryptic polyadenylation signals are widely distributed over the intron sequences of Drosophila melanogaster. As shown by analyzing the distribution of genes arranged in a nested pattern, where one gene is fully located within an intron of another gene, overlapping of putative polyadenylation signals is a fairly common event affecting about 17% of all genes. Here we show that polyadenylation signals are silenced within introns: the poly(A) signal is utilized in the exonic but not in the intronic regions of the transcript. The transcription does not end within the introns, either in a transient reporter system or in the genomic context, while deletion of the 5'-splice site restores their functionality. According to a full Drosophila transcriptome analysis, utilization of intronic polyadenylation signals occurs very rarely and such events are likely to be inducible. These results confirm that the transcription apparatus ignores premature polyadenylation signals for as long as they are intronic.
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Affiliation(s)
- M. Tikhonov
- Department of the Control of Genetic Processes, Institute of Gene Biology, Russian Academy of Sciences, 34/5 Vavilova Str., Moscow, Russia, 119334
| | - P. Georgiev
- Department of the Control of Genetic Processes, Institute of Gene Biology, Russian Academy of Sciences, 34/5 Vavilova Str., Moscow, Russia, 119334
| | - O. Maksimenko
- Department of the Control of Genetic Processes, Institute of Gene Biology, Russian Academy of Sciences, 34/5 Vavilova Str., Moscow, Russia, 119334
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19
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Pandya-Jones A, Bhatt DM, Lin CH, Tong AJ, Smale ST, Black DL. Splicing kinetics and transcript release from the chromatin compartment limit the rate of Lipid A-induced gene expression. RNA (NEW YORK, N.Y.) 2013; 19:811-27. [PMID: 23616639 PMCID: PMC3683915 DOI: 10.1261/rna.039081.113] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/27/2013] [Accepted: 03/13/2013] [Indexed: 05/26/2023]
Abstract
The expression of eukaryotic mRNAs is achieved though an intricate series of molecular processes that provide many steps for regulating the production of a final gene product. However, the relationships between individual steps in mRNA biosynthesis and the rates at which they occur are poorly understood. By applying RNA-seq to chromatin-associated and soluble nucleoplasmic fractions of RNA from Lipid A-stimulated macrophages, we examined the timing of exon ligation and transcript release from chromatin relative to the induction of transcription. We find that for a subset of genes in the Lipid A response, the ligation of certain exon pairs is delayed relative to the synthesis of the complete transcript. In contrast, 3' end cleavage and polyadenylation occur rapidly once transcription extends through the cleavage site. Our data indicate that these transcripts with delayed splicing are not released from the chromatin fraction until all the introns have been excised. These unusual kinetics result in a chromatin-associated pool of completely transcribed and 3'-processed transcripts that are not yet fully spliced. We also find that long introns containing repressed exons that will be excluded from the final mRNA are excised particularly slowly relative to other introns in a transcript. These results indicate that the kinetics of splicing and transcript release contribute to the timing of expression for multiple genes of the inflammatory response.
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Affiliation(s)
- Amy Pandya-Jones
- Department of Microbiology, Immunology and Molecular Genetics, University of California, Los Angeles, California 90025, USA
- Molecular Biology Institute, University of California, Los Angeles, California 90025, USA
| | - Dev M. Bhatt
- Department of Microbiology, Immunology and Molecular Genetics, University of California, Los Angeles, California 90025, USA
- Molecular Biology Institute, University of California, Los Angeles, California 90025, USA
| | - Chia-Ho Lin
- Department of Microbiology, Immunology and Molecular Genetics, University of California, Los Angeles, California 90025, USA
| | - Ann-Jay Tong
- Department of Microbiology, Immunology and Molecular Genetics, University of California, Los Angeles, California 90025, USA
- Molecular Biology Institute, University of California, Los Angeles, California 90025, USA
| | - Stephen T. Smale
- Department of Microbiology, Immunology and Molecular Genetics, University of California, Los Angeles, California 90025, USA
- Molecular Biology Institute, University of California, Los Angeles, California 90025, USA
| | - Douglas L. Black
- Department of Microbiology, Immunology and Molecular Genetics, University of California, Los Angeles, California 90025, USA
- Molecular Biology Institute, University of California, Los Angeles, California 90025, USA
- Howard Hughes Medical Institute, University of California, Los Angeles, California 90025, USA
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20
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Schrom EM, Moschall R, Hartl MJ, Weitner H, Fecher D, Langemeier J, Bohne J, Wöhrl BM, Bodem J. U1snRNP-mediated suppression of polyadenylation in conjunction with the RNA structure controls poly (A) site selection in foamy viruses. Retrovirology 2013; 10:55. [PMID: 23718736 PMCID: PMC3694450 DOI: 10.1186/1742-4690-10-55] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2012] [Accepted: 05/21/2013] [Indexed: 11/13/2022] Open
Abstract
Background During reverse transcription, retroviruses duplicate the long terminal repeats (LTRs). These identical LTRs carry both promoter regions and functional polyadenylation sites. To express full-length transcripts, retroviruses have to suppress polyadenylation in the 5′LTR and activate polyadenylation in the 3′LTR. Foamy viruses have a unique LTR structure with respect to the location of the major splice donor (MSD), which is located upstream of the polyadenylation signal. Results Here, we describe the mechanisms of foamy viruses regulating polyadenylation. We show that binding of the U1 small nuclear ribonucleoprotein (U1snRNP) to the MSD suppresses polyadenylation at the 5′LTR. In contrast, polyadenylation at the 3′LTR is achieved by adoption of a different RNA structure at the MSD region, which blocks U1snRNP binding and furthers RNA cleavage and subsequent polyadenylation. Conclusion Recently, it was shown that U1snRNP is able to suppress the usage of intronic cryptic polyadenylation sites in the cellular genome. Foamy viruses take advantage of this surveillance mechanism to suppress premature polyadenylation at the 5’end of their RNA. At the 3’end, Foamy viruses use a secondary structure to presumably block access of U1snRNP and thereby activate polyadenylation at the end of the genome. Our data reveal a contribution of U1snRNP to cellular polyadenylation site selection and to the regulation of gene expression.
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Affiliation(s)
- Eva-Maria Schrom
- Institute of Virology and Immunobiology, University of Würzburg, Würzburg, Germany
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21
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Andersen PK, Jensen TH, Lykke-Andersen S. Making ends meet: coordination between RNA 3'-end processing and transcription initiation. WILEY INTERDISCIPLINARY REVIEWS-RNA 2013; 4:233-46. [PMID: 23450686 DOI: 10.1002/wrna.1156] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
RNA polymerase II (RNAPII)-mediated gene transcription initiates at promoters and ends at terminators. Transcription termination is intimately connected to 3'-end processing of the produced RNA and already when loaded at the promoter, RNAPII starts to become configured for this downstream event. Conversely, RNAPII is 'reset' as part of the 3'-end processing/termination event, thus preparing the enzyme for its next round of transcription--possibly on the same gene. There is both direct and circumstantial evidence for preferential recycling of RNAPII from the gene terminator back to its own promoter, which supposedly increases the efficiency of the transcription process under conditions where RNAPII levels are rate limiting. Here, we review differences and commonalities between initiation and 3'-end processing/termination processes on various types of RNAPII transcribed genes. In doing so, we discuss the requirements for efficient 3'-end processing/termination and how these may relate to proper recycling of RNAPII.
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Affiliation(s)
- Pia K Andersen
- Centre for mRNP Biogenesis and Metabolism, Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark
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22
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Autoregulation of TDP-43 mRNA levels involves interplay between transcription, splicing, and alternative polyA site selection. Genes Dev 2012; 26:1679-84. [PMID: 22855830 DOI: 10.1101/gad.194829.112] [Citation(s) in RCA: 137] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
TDP-43 is a critical RNA-binding factor associated with pre-mRNA splicing in mammals. Its expression is tightly autoregulated, with loss of this regulation implicated in human neuropathology. We demonstrate that TDP-43 overexpression in humans and mice activates a 3' untranslated region (UTR) intron, resulting in excision of the proximal polyA site (PAS) pA(1). This activates a cryptic PAS that prevents TDP-43 expression through a nuclear retention mechanism. Superimposed on this process, overexpression of TDP-43 blocks recognition of pA(1) by competing with CstF-64 for PAS binding. Overall, we uncover complex interplay between transcription, splicing, and 3' end processing to effect autoregulation of TDP-43.
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23
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Schmid M, Jensen TH. Transcription-associated quality control of mRNP. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2012; 1829:158-68. [PMID: 22982197 DOI: 10.1016/j.bbagrm.2012.08.012] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/26/2012] [Revised: 08/24/2012] [Accepted: 08/29/2012] [Indexed: 01/06/2023]
Abstract
Although a prime purpose of transcription is to produce RNA, a substantial amount of transcript is nevertheless turned over very early in its lifetime. During transcription RNAs are matured by nucleases from longer precursors and activities are also employed to exert quality control over the RNA synthesis process so as to discard, retain or transcriptionally silence unwanted molecules. In this review we discuss the somewhat paradoxical circumstance that the retention or turnover of RNA is often linked to its synthesis. This occurs via the association of chromatin, or the transcription elongation complex, with RNA degradation (co)factors. Although our main focus is on protein-coding genes, we also discuss mechanisms of transcription-connected turnover of non-protein-coding RNA from where important general principles are derived. This article is part of a Special Issue entitled: RNA polymerase II Transcript Elongation.
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Affiliation(s)
- Manfred Schmid
- Department of Molecular Biology and Genetics, Aarhus University, Aarhus C., Denmark
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24
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Barbrook AC, Dorrell RG, Burrows J, Plenderleith LJ, Nisbet RER, Howe CJ. Polyuridylylation and processing of transcripts from multiple gene minicircles in chloroplasts of the dinoflagellate Amphidinium carterae. PLANT MOLECULAR BIOLOGY 2012; 79:347-57. [PMID: 22562591 DOI: 10.1007/s11103-012-9916-z] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2012] [Accepted: 04/14/2012] [Indexed: 05/03/2023]
Abstract
Although transcription and transcript processing in the chloroplasts of plants have been extensively characterised, the RNA metabolism of other chloroplast lineages across the eukaryotes remains poorly understood. In this paper, we use RT-PCR to study transcription and transcript processing in the chloroplasts of Amphidinium carterae, a model peridinin-containing dinoflagellate. These organisms have a highly unusual chloroplast genome, with genes located on multiple small 'minicircle' elements, and a number of idiosyncratic features of RNA metabolism including transcription via a rolling circle mechanism, and 3' terminal polyuridylylation of transcripts. We demonstrate that transcription occurs in A. carterae via a rolling circle mechanism, as previously shown in the dinoflagellate Heterocapsa, and present evidence for the production of both polycistronic and monocistronic transcripts from A. carterae minicircles, including several regions containing ORFs previously not known to be expressed. We demonstrate the presence of both polyuridylylated and non-polyuridylylated transcripts in A. carterae, and show that polycistronic transcripts can be terminally polyuridylylated. We present a model for RNA metabolism in dinoflagellate chloroplasts where long polycistronic precursors are processed to form mature transcripts. Terminal polyuridylylation may mark transcripts with the correct 3' end.
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MESH Headings
- Chloroplasts/genetics
- DNA, Circular/genetics
- DNA, Circular/metabolism
- DNA, Protozoan/genetics
- DNA, Protozoan/metabolism
- Dinoflagellida/genetics
- Dinoflagellida/metabolism
- Genes, Chloroplast
- Genes, Protozoan
- Models, Biological
- Poly U/metabolism
- RNA Processing, Post-Transcriptional
- RNA, Protozoan/genetics
- RNA, Protozoan/metabolism
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Affiliation(s)
- Adrian C Barbrook
- Department of Biochemistry, University of Cambridge, Building O, Downing Site, Tennis Court Road, Cambridge, CB2 1QW, UK.
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25
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Abstract
Foamy viruses (FVs) are distinct members of the retrovirus (RV) family. In this chapter, the molecular regulation of foamy viral transcription, splicing, polyadenylation, and RNA export will be compared in detail to the orthoretroviruses. Foamy viral transcription is regulated in early and late phases, which are separated by the usage of two promoters. The viral transactivator protein Tas activates both promoters. The nature of this early-late switch and the molecular mechanism used by Tas are unique among RVs. RVs duplicate the long terminal repeats (LTRs) during reverse transcription. These LTRs carry both a promoter region and functional poly(A) sites. In order to express full-length transcripts, RVs have to silence the poly(A) signal in the 5' LTR and to activate it in the 3' LTR. FVs have a unique R-region within these LTRs with a major splice donor (MSD) at +51 followed by a poly(A) signal. FVs use a MSD-dependent mechanism to inactivate the polyadenylation. Most RVs express all their genes from a single primary transcript. In order to allow expression of more than one gene from this RNA, differential splicing is extensively used in complex RVs. The splicing pattern of FV is highly complex. In contrast to orthoretroviruses, FVs synthesize the Pol precursor protein from a specific and spliced transcript. The LTR and IP-derived primary transcripts are spliced into more than 15 different mRNA species. Since the RNA ratios have to be balanced, a tight regulation of splicing is required. Cellular quality control mechanisms retain and degrade unspliced or partially spliced RNAs in the nucleus. In this review, I compare the RNA export pathways used by orthoretroviruses with the distinct RNA export pathway used by FV. All these steps are highly regulated by host and viral factors and set FVs apart from all other RVs.
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Affiliation(s)
- Jochen Bodem
- Institute of Virology and Immunobiology, University of Würzburg, Würzburg, Germany
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26
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Vargas DY, Shah K, Batish M, Levandoski M, Sinha S, Marras SAE, Schedl P, Tyagi S. Single-molecule imaging of transcriptionally coupled and uncoupled splicing. Cell 2012; 147:1054-65. [PMID: 22118462 DOI: 10.1016/j.cell.2011.10.024] [Citation(s) in RCA: 146] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2010] [Revised: 06/28/2011] [Accepted: 10/24/2011] [Indexed: 12/18/2022]
Abstract
Introns are removed from pre-mRNAs during transcription while the pre-mRNA is still tethered to the gene locus via RNA polymerase. However, during alternative splicing, it is important that splicing be deferred until all of the exons and introns involved in the choice have been synthesized. We have developed an in situ RNA imaging method with single-molecule sensitivity to define the intracellular sites of splicing. Using this approach, we found that the normally tight coupling between transcription and splicing is broken in situations where the intron's polypyrimidine tract is sequestered within strong secondary structures. We also found that in two cases of alternative splicing, in which certain exons are skipped due to the activity of the RNA-binding proteins Sxl and PTB, splicing is uncoupled from transcription. This uncoupling occurs only on the perturbed introns, whereas the preceding and succeeding introns are removed cotranscriptionally. PAPERCLIP:
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Affiliation(s)
- Diana Y Vargas
- Public Health Research Institute, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark, NJ 07103, USA
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27
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Aitken S, Alexander RD, Beggs JD. Modelling reveals kinetic advantages of co-transcriptional splicing. PLoS Comput Biol 2011; 7:e1002215. [PMID: 22022255 PMCID: PMC3192812 DOI: 10.1371/journal.pcbi.1002215] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2011] [Accepted: 08/16/2011] [Indexed: 01/21/2023] Open
Abstract
Messenger RNA splicing is an essential and complex process for the removal of intron sequences. Whereas the composition of the splicing machinery is mostly known, the kinetics of splicing, the catalytic activity of splicing factors and the interdependency of transcription, splicing and mRNA 3′ end formation are less well understood. We propose a stochastic model of splicing kinetics that explains data obtained from high-resolution kinetic analyses of transcription, splicing and 3′ end formation during induction of an intron-containing reporter gene in budding yeast. Modelling reveals co-transcriptional splicing to be the most probable and most efficient splicing pathway for the reporter transcripts, due in part to a positive feedback mechanism for co-transcriptional second step splicing. Model comparison is used to assess the alternative representations of reactions. Modelling also indicates the functional coupling of transcription and splicing, because both the rate of initiation of transcription and the probability that step one of splicing occurs co-transcriptionally are reduced, when the second step of splicing is abolished in a mutant reporter. The coding information for the synthesis of proteins in mammalian cells is first transcribed from DNA to messenger RNA (mRNA), before being translated from mRNA to protein. Each step is complex, and subject to regulation. Certain sequences of DNA must be skipped in order to generate a functional protein, and these sequences, known as introns, are removed from the mRNA by the process of splicing. Splicing is well understood in terms of the proteins and complexes that are involved, but the rates of reactions, and models for the splicing pathways, have not yet been established. We present a model of splicing in yeast that accounts for the possibilities that splicing may take place while the mRNA is in the process of being created, as well as the possibility that splicing takes place once mRNA transcription is complete. We assign rates to the reactions in the pathway, and show that co-transcriptional splicing is the preferred pathway. In order to reach these conclusions, we compare a number of alternative models by a quantitative computational method. Our analysis relies on the quantitative measurement of messenger RNA in live cells - this is a major challenge in itself that has only recently been addressed.
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Affiliation(s)
- Stuart Aitken
- Centre for Systems Biology, University of Edinburgh, Edinburgh, United Kingdom.
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28
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Singh NN, Singh RN. Alternative splicing in spinal muscular atrophy underscores the role of an intron definition model. RNA Biol 2011; 8:600-6. [PMID: 21654213 DOI: 10.4161/rna.8.4.16224] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Humans have two nearly identical copies of the Survival Motor Neuron (SMN) gene: SMN1 and SMN2. The two SMN genes code for identical proteins; however, SMN2 predominantly generates a shorter transcript due to skipping of exon 7, the last coding exon. Skipping of SMN2 exon 7 leads to production of a truncated SMN protein that is highly unstable. The inability of SMN2 to compensate for the loss of SMN1 results in spinal muscular atrophy (SMA), the second most prevalent genetic cause of infant mortality. Since SMN2 is almost universally present in SMA patients, correction of SMN2 exon 7 splicing holds the promise for cure. Consistently, SMN2 exon 7 splicing has emerged as one of the best studied splicing systems in humans. The vast amount of recent literature provides a clue that SMN2 exon 7 splicing is regulated by an intron definition mechanism, which does not require cross-exon communication as prerequisite for exon inclusion. Our conclusion is based on the prominent role of intronic cis-elements, some of them have emerged as the frontrunners among potential therapeutic targets of SMA. Further, the widely expressed T-cell-restricted intracellular antigen-1 (TIA1), a member of the Q-rich domain containing RNA-binding proteins, has recently been found to regulate SMN exon 7 splicing by binding to intron 7 sequences away from the 5′ ss. These findings make a strong argument for an "intron definition model", according to which regulatory sequences within a downstream intron are capable of enforcing exon inclusion even in the absence of a defined upstream 3′ ss of an alternatively spliced exon.
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Affiliation(s)
- Natalia N Singh
- Department of Biomedical Sciences Iowa State University, Ames, IA, USA
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29
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Gencheva M, Lin TY, Wu X, Yang L, Richard C, Jones M, Lin SB, Lin RJ. Nuclear retention of unspliced pre-mRNAs by mutant DHX16/hPRP2, a spliceosomal DEAH-box protein. J Biol Chem 2010; 285:35624-32. [PMID: 20841358 DOI: 10.1074/jbc.m110.122309] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Defective or imbalanced expression of spliceosomal factors has been linked to human disease; however, how a defective spliceosome affects intron-containing gene transcripts in human cells is largely unknown. DEAH-box protein DHX16 is a human orthologue of Saccharomyces cerevisiae spliceosomal protein Prp2, an RNA-dependent ATPase that activates the spliceosome before the first catalytic step of splicing. Yeast prp2 mutants accumulate unspliced RNAs from the vast majority of intron-containing genes. Here we used a genomic tiling microarray to screen transcripts from four chromosomes in human cells expressing a dominant negative DHX16 mutant and identified a number of gene transcripts that retained their introns. The mutant protein also affected gene transcripts that are sensitive to pladienolide, an SF3b inhibitor. The unspliced RNAs were retained in the nucleus, and block of nonsense-mediated decay did not affect their accumulation. Thus, a perturbation of human PRP2/DHX16 results in accumulation of unspliced transcripts, similar to the outcome in yeast prp2 mutants. The results further suggest that mutant DHX16/hPRP2 causes a defective spliceosome to retain unspliced gene transcripts in the nuclei of human cells.
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Affiliation(s)
- Marieta Gencheva
- Department of Molecular and Cellular Biology, Beckman Research Institute of the City of Hope, Duarte, California 91010, USA
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30
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Kazerouninia A, Ngo B, Martinson HG. Poly(A) signal-dependent degradation of unprocessed nascent transcripts accompanies poly(A) signal-dependent transcriptional pausing in vitro. RNA (NEW YORK, N.Y.) 2010; 16:197-210. [PMID: 19926725 PMCID: PMC2802029 DOI: 10.1261/rna.1622010] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2009] [Accepted: 09/22/2009] [Indexed: 05/28/2023]
Abstract
The poly(A) signal has long been known for its role in directing the cleavage and polyadenylation of eukaryotic mRNA. In recent years its additional coordinating role in multiple related aspects of gene expression has also become increasingly clear. Here we use HeLa nuclear extracts to study two of these activities, poly(A) signal-dependent transcriptional pausing, which was originally proposed as a surveillance checkpoint, and poly(A) signal-dependent degradation (PDD) of unprocessed transcripts from weak poly(A) signals. We confirm directly, by measuring the length of RNA within isolated transcription elongation complexes, that a newly transcribed poly(A) signal reduces the rate of elongation by RNA polymerase II and causes the accumulation of elongation complexes downstream from the poly(A) signal. We then show that if the RNA in these elongation complexes contains a functional but unprocessed poly(A) signal, degradation of the transcripts ensues. The degradation depends on the unprocessed poly(A) signal being functional, and does not occur if a mutant poly(A) signal is used. We suggest that during normal 3'-end processing the uncleaved poly(A) signal continuously samples competing reaction pathways for processing and for degradation, and that in the case of weak poly(A) signals, where poly(A) site cleavage is slow, the default pathway to degradation predominates.
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Affiliation(s)
- Amir Kazerouninia
- Department of Chemistry and Biochemistry, University of California at Los Angeles, Los Angeles, California 90095-1569, USA
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31
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Pawlicki JM, Steitz JA. Nuclear networking fashions pre-messenger RNA and primary microRNA transcripts for function. Trends Cell Biol 2009; 20:52-61. [PMID: 20004579 DOI: 10.1016/j.tcb.2009.10.004] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2009] [Revised: 10/15/2009] [Accepted: 10/20/2009] [Indexed: 10/20/2022]
Abstract
The expression of protein-coding genes is enhanced by the exquisite coupling of transcription by RNA polymerase II with pre-messenger RNA processing reactions, such as 5'-end capping, splicing and 3'-end formation. Integration between cotranscriptional processing events extends beyond the nucleus, as proteins that bind cotranscriptionally can affect the localization, translation and degradation of the mature messenger RNA. MicroRNAs are RNA polymerase II transcripts with crucial roles in the regulation of gene expression. Recent data demonstrate that processing of primary microRNA transcripts might be yet another cotranscriptional event that is woven into this elaborate nuclear network. This review discusses the extensive molecular interactions that couple the earliest steps in gene expression and therefore influence the final fate and function of the mature messenger RNA or microRNA produced.
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Affiliation(s)
- Jan M Pawlicki
- Department of Molecular Biophysics and Biochemistry, Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06536, USA
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32
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Perales R, Bentley D. "Cotranscriptionality": the transcription elongation complex as a nexus for nuclear transactions. Mol Cell 2009; 36:178-91. [PMID: 19854129 DOI: 10.1016/j.molcel.2009.09.018] [Citation(s) in RCA: 286] [Impact Index Per Article: 19.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2009] [Revised: 07/07/2009] [Accepted: 08/06/2009] [Indexed: 12/27/2022]
Abstract
Much of the complex process of RNP biogenesis takes place at the gene cotranscriptionally. The target for RNA binding and processing factors is, therefore, not a solitary RNA molecule but, rather, a transcription elongation complex (TEC) comprising the growing nascent RNA and RNA polymerase traversing a chromatin template with associated passenger proteins. RNA maturation factors are not the only nuclear machines whose work is organized cotranscriptionally around the TEC scaffold. Additionally, DNA repair, covalent chromatin modification, "gene gating" at the nuclear pore, Ig gene hypermutation, and sister chromosome cohesion have all been demonstrated or suggested to involve a cotranscriptional component. From this perspective, TECs can be viewed as potent "community organizers" within the nucleus.
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Affiliation(s)
- Roberto Perales
- Department of Biochemistry and Molecular Genetics, University of Colorado School of Medicine, UCHSC, MS8101, P.O. Box 6511, Aurora CO, 80045, USA
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Barlow CA, Laishram RS, Anderson RA. Nuclear phosphoinositides: a signaling enigma wrapped in a compartmental conundrum. Trends Cell Biol 2009; 20:25-35. [PMID: 19846310 DOI: 10.1016/j.tcb.2009.09.009] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2009] [Revised: 09/27/2009] [Accepted: 09/28/2009] [Indexed: 01/09/2023]
Abstract
While the presence of phosphoinositides in the nuclei of eukaryotes and the identity of the enzymes responsible for their metabolism have been known for some time, their functions in the nucleus are only now emerging. This is illustrated by the recent identification of effectors for nuclear phosphoinositides. Like the cytosolic phosphoinositide signaling pathway, nuclear phosphatidylinositol 4,5-bisphosphate (PI4,5P(2)) is at the center of the pathway and acts both as a messenger and as a precursor for many additional messengers. Here, recent advances in the understanding of nuclear phosphoinositide signaling and its functions are reviewed with an emphasis on PI4,5P(2) and its role in gene expression. The compartmentalization of nuclear phosphoinositide phosphates (PIP(n)) remains a mystery, but emerging evidence suggests that phosphoinositides occupy several functionally distinct compartments.
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Affiliation(s)
- Christy A Barlow
- University of Wisconsin-Madison, Department of Pharmacology, 1300 University Ave. University of Wisconsin Medical School, Madison, WI 53706, USA
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Pandya-Jones A, Black DL. Co-transcriptional splicing of constitutive and alternative exons. RNA (NEW YORK, N.Y.) 2009; 15:1896-908. [PMID: 19656867 PMCID: PMC2743041 DOI: 10.1261/rna.1714509] [Citation(s) in RCA: 215] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/30/2009] [Accepted: 06/25/2009] [Indexed: 05/17/2023]
Abstract
In metazoan organisms, pre-mRNA splicing is thought to occur during transcription, and it is postulated that these two processes are functionally coupled via still-unknown mechanisms. Current evidence supports co-transcriptional spliceosomal assembly, but there is little quantitative information on how much splicing is completed during RNA synthesis. Here we isolate nascent chromatin-associated RNA from free, nucleoplasmic RNA already released from the DNA template. Using a quantitative RT-PCR assay, we show that the majority of introns separating constitutive exons are already excised from the human c-Src and fibronectin pre-mRNAs that are still in the process of synthesis, and that these introns are removed in a general 5'-to-3' order. Introns flanking alternative exons in these transcripts are also removed during synthesis, but show differences in excision efficiency between cell lines with different regulatory conditions. Our data suggest that skipping of an exon can induce a lag in splicing compared to intron removal under conditions of exon inclusion. Nevertheless, excision of the long intron encompassing the skipped exon is still completed prior to transcript release into the nucleoplasm. Thus, we demonstrate that the decision to include or skip an alternative exon is made during transcription and not post-transcriptionally.
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Affiliation(s)
- Amy Pandya-Jones
- Department of Microbiology, Immunology and Molecular Genetics, University of California at Los Angeles, Los Angeles, California 90095, USA
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Haenni S, Sharpe HE, Gravato Nobre M, Zechner K, Browne C, Hodgkin J, Furger A. Regulation of transcription termination in the nematode Caenorhabditis elegans. Nucleic Acids Res 2009; 37:6723-36. [PMID: 19740764 PMCID: PMC2777434 DOI: 10.1093/nar/gkp744] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The current predicted mechanisms that describe RNA polymerase II (pol II) transcription termination downstream of protein expressing genes fail to adequately explain, how premature termination is prevented in eukaryotes that possess operon-like structures. Here we address this issue by analysing transcription termination at the end of single protein expressing genes and genes located within operons in the nematode Caenorhabditis elegans. By using a combination of RT-PCR and ChIP analysis we found that pol II generally transcribes up to 1 kb past the poly(A) sites into the 3' flanking regions of the nematode genes before it terminates. We also show that pol II does not terminate after transcription of internal poly(A) sites in operons. We provide experimental evidence that five randomly chosen C. elegans operons are transcribed as polycistronic pre-mRNAs. Furthermore, we show that cis-splicing of the first intron located in downstream positioned genes in these polycistronic pre-mRNAs is critical for their expression and may play a role in preventing premature pol II transcription termination.
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Affiliation(s)
- Simon Haenni
- Genetics Unit, Department of Biochemistry, University of Oxford, Oxford OX1 3QU, UK
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