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Mayán MD. RNAP-II transcribes two small RNAs at the promoter and terminator regions of the RNAP-I gene in Saccharomyces cerevisiae. Yeast 2012; 30:25-32. [PMID: 23280698 DOI: 10.1002/yea.2938] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2012] [Accepted: 11/13/2012] [Indexed: 11/11/2022] Open
Abstract
Three RNA polymerases coexist in the ribosomal DNA of Saccharomyces cerevisiae. RNAP-I transcribes the 35S rRNA, RNAP-III transcribes the 5S rRNA and RNAP-II is found in both intergenic non-coding regions. Previously, we demonstrated that RNAP-II molecules bound to the intergenic non-coding regions (IGS) of the ribosomal locus are mainly found in a stalled conformation, and the stalled polymerase mediates chromatin interactions, which isolate RNAP-I from the RNAP-III transcriptional domain. Besides, RNAP-II transcribes both IGS regions at low levels, using different cryptic promoters. This report demonstrates that RNAP-II also transcribes two sequences located in the 5'- and 3'-ends of the 35S rRNA gene that overlap with the sequences of the 35S rRNA precursor transcribed by RNAP-I. The sequence located at the promoter region of RNAP-I, called the p-RNA transcript, binds to the transcription termination-related protein, Reb1p, while the T-RNA sequence, located in the termination sites of RNAP-I gene, contains the stem-loop recognized by Rtn1p, which is necessary for proper termination of RNAP-I. Because of their location, these small RNAs may play a key role in the initiation and termination of RNAP-I transcription. To correctly synthesize proteins, eukaryotic cells may retain a mechanism that connects the three main polymerases. This report suggests that cryptic transcription by RNAP-II may be required for normal transcription by RNAP-I in the ribosomal locus of S. cerevisiae.
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Affiliation(s)
- Maria D Mayán
- MRC Clinical Sciences Centre, Imperial College, London, UK.
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52
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Sentenac A, Riva M. Odd RNA polymerases or the A(B)C of eukaryotic transcription. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2012; 1829:251-7. [PMID: 23142548 DOI: 10.1016/j.bbagrm.2012.10.012] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2012] [Revised: 10/29/2012] [Accepted: 10/30/2012] [Indexed: 02/08/2023]
Abstract
Pioneering studies on eukaryotic transcription were undertaken with the bacterial system in mind. Will the bacterial paradigm apply to eukaryotes? Are there promoter sites scattered in the eukaryotic genome, and sigma-like proteins? Why three forms of RNA polymerase in eukaryotic cells? Why are they structurally so complex, in particular RNA polymerases I and III, compared to the bacterial enzyme? These questions and others that were raised along the way are evoked in this short historical survey of odd RNA polymerases studies, with some emphasis on the contribution of these studies to our global understanding of eukaryotic transcription systems. This article is part of a Special Issue entitled: Transcription by Odd Pols.
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Affiliation(s)
- André Sentenac
- CEA-Saclay, iBiTecS, F-91191 Gif-sur-Yvette cedex, France.
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53
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Németh A, Perez-Fernandez J, Merkl P, Hamperl S, Gerber J, Griesenbeck J, Tschochner H. RNA polymerase I termination: Where is the end? BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2012; 1829:306-17. [PMID: 23092677 DOI: 10.1016/j.bbagrm.2012.10.007] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/06/2012] [Revised: 10/10/2012] [Accepted: 10/17/2012] [Indexed: 01/01/2023]
Abstract
The synthesis of ribosomal RNA (rRNA) precursor molecules by RNA polymerase I (Pol I) terminates with the dissociation of the protein-DNA-RNA ternary complex. Based on in vitro results the mechanism of Pol I termination appeared initially to be rather conserved and simple until this process was more thoroughly re-investigated in vivo. A picture emerged that Pol I termination seems to be connected to co-transcriptional processing, re-initiation of transcription and, possibly, other processes downstream of Pol I transcription units. In this article, our current understanding of the mechanism of Pol I termination and how this process might be implicated in other biological processes in yeast and mammals is summarized and discussed. This article is part of a Special Issue entitled: Transcription by Odd Pols.
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Affiliation(s)
- Attila Németh
- Universität Regensburg, Biochemie-Zentrum Regensburg (BZR), Lehrstuhl Biochemie III, 93053 Regensburg, Germany.
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Epigenetic control of RNA polymerase I transcription in mammalian cells. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2012; 1829:393-404. [PMID: 23063748 DOI: 10.1016/j.bbagrm.2012.10.004] [Citation(s) in RCA: 103] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2012] [Revised: 10/04/2012] [Accepted: 10/06/2012] [Indexed: 11/22/2022]
Abstract
rRNA synthesis is regulated by genetic and epigenetic mechanisms. Epigenetic states are metastable, changing in response to appropriate signals, thereby modulating transcription in vivo. The establishment, maintenance and reversal of epigenetic features are fundamental for the cell's ability to 'remember' past events, to adapt to environmental changes or developmental cues and to propagate this information to the progeny. As packaging into chromatin is critical for the stability and integrity of repetitive DNA, keeping a fraction of rRNA genes in a metastable heterochromatic conformation prevents aberrant exchanges between repeats, thus safeguarding nucleolar structure and rDNA stability. In this review, we will focus on the nature of the molecular signatures that characterize a given epigenetic state of rDNA in mammalian cells, including noncoding RNA, DNA methylation and histone modifications, and the mechanisms by which they are established and maintained. This article is part of a Special Issue entitled: Transcription by Odd Pols.
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55
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Cong R, Das S, Ugrinova I, Kumar S, Mongelard F, Wong J, Bouvet P. Interaction of nucleolin with ribosomal RNA genes and its role in RNA polymerase I transcription. Nucleic Acids Res 2012; 40:9441-54. [PMID: 22859736 PMCID: PMC3479187 DOI: 10.1093/nar/gks720] [Citation(s) in RCA: 109] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2011] [Revised: 06/04/2012] [Accepted: 07/04/2012] [Indexed: 12/13/2022] Open
Abstract
Nucleolin is a multi-functional nucleolar protein that is required for ribosomal RNA gene (rRNA) transcription in vivo, but the mechanism by which nucleolin modulates RNA polymerase I (RNAPI) transcription is not well understood. Nucleolin depletion results in an increase in the heterochromatin mark H3K9me2 and a decrease in H4K12Ac and H3K4me3 euchromatin histone marks in rRNA genes. ChIP-seq experiments identified an enrichment of nucleolin in the ribosomal DNA (rDNA) coding and promoter region. Nucleolin is preferentially associated with unmethylated rRNA genes and its depletion leads to the accumulation of RNAPI at the beginning of the transcription unit and a decrease in UBF along the coding and promoter regions. Nucleolin is able to affect the binding of transcription termination factor-1 on the promoter-proximal terminator T0, thus inhibiting the recruitment of TIP5 and HDAC1 and the establishment of a repressive heterochromatin state. These results reveal the importance of nucleolin for the maintenance of the euchromatin state and transcription elongation of rDNA.
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Affiliation(s)
- Rong Cong
- Université de Lyon, Ecole Normale Supérieure de Lyon, CNRS USR 3010, Laboratoire Joliot-Curie, 69364 Lyon, France, The Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai 200241, China and BioCOS Life Sciences Private Limited, Biotech Park, Electronics City, Phase-1, Bangalore 560100, India
| | - Sadhan Das
- Université de Lyon, Ecole Normale Supérieure de Lyon, CNRS USR 3010, Laboratoire Joliot-Curie, 69364 Lyon, France, The Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai 200241, China and BioCOS Life Sciences Private Limited, Biotech Park, Electronics City, Phase-1, Bangalore 560100, India
| | - Iva Ugrinova
- Université de Lyon, Ecole Normale Supérieure de Lyon, CNRS USR 3010, Laboratoire Joliot-Curie, 69364 Lyon, France, The Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai 200241, China and BioCOS Life Sciences Private Limited, Biotech Park, Electronics City, Phase-1, Bangalore 560100, India
| | - Sanjeev Kumar
- Université de Lyon, Ecole Normale Supérieure de Lyon, CNRS USR 3010, Laboratoire Joliot-Curie, 69364 Lyon, France, The Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai 200241, China and BioCOS Life Sciences Private Limited, Biotech Park, Electronics City, Phase-1, Bangalore 560100, India
| | - Fabien Mongelard
- Université de Lyon, Ecole Normale Supérieure de Lyon, CNRS USR 3010, Laboratoire Joliot-Curie, 69364 Lyon, France, The Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai 200241, China and BioCOS Life Sciences Private Limited, Biotech Park, Electronics City, Phase-1, Bangalore 560100, India
| | - Jiemin Wong
- Université de Lyon, Ecole Normale Supérieure de Lyon, CNRS USR 3010, Laboratoire Joliot-Curie, 69364 Lyon, France, The Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai 200241, China and BioCOS Life Sciences Private Limited, Biotech Park, Electronics City, Phase-1, Bangalore 560100, India
| | - Philippe Bouvet
- Université de Lyon, Ecole Normale Supérieure de Lyon, CNRS USR 3010, Laboratoire Joliot-Curie, 69364 Lyon, France, The Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai 200241, China and BioCOS Life Sciences Private Limited, Biotech Park, Electronics City, Phase-1, Bangalore 560100, India
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The Reb1-homologue Ydr026c/Nsi1 is required for efficient RNA polymerase I termination in yeast. EMBO J 2012; 31:3480-93. [PMID: 22805593 DOI: 10.1038/emboj.2012.185] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2012] [Accepted: 06/19/2012] [Indexed: 12/27/2022] Open
Abstract
Several DNA cis-elements and trans-acting factors were described to be involved in transcription termination and to release the elongating RNA polymerases from their templates. Different models for the molecular mechanism of transcription termination have been suggested for eukaryotic RNA polymerase I (Pol I) from results of in vitro and in vivo experiments. To analyse the molecular requirements for yeast RNA Pol I termination, an in vivo approach was used in which efficient termination resulted in growth inhibition. This led to the identification of a Myb-like protein, Ydr026c, as bona fide termination factor, now designated Nsi1 (NTS1 silencing protein 1), since it was very recently described as silencing factor of ribosomal DNA. Possible Nsi1 functions in regard to the mechanism of transcription termination are discussed.
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Tan BCM, Yang CC, Hsieh CL, Chou YH, Zhong CZ, Yung BYM, Liu H. Epigeneitc silencing of ribosomal RNA genes by Mybbp1a. J Biomed Sci 2012; 19:57. [PMID: 22686419 PMCID: PMC3407492 DOI: 10.1186/1423-0127-19-57] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2011] [Accepted: 06/11/2012] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Transcription of the ribosomal RNA gene repeats by Pol I occurs in the nucleolus and is a fundamental step in ribosome biogenesis and protein translation. Due to tight coordination between ribosome biogenesis and cell proliferation, transcription of rRNA and stable maintenance of rDNA clusters are thought to be under intricate control by intercalated mechanisms, particularly at the epigenetic level. METHODS AND RESULTS Here we identify the nucleolar protein Myb-binding protein 1a (Mybbp1a) as a novel negative regulator of rRNA expression. Suppression of rDNA transcription by Mybbp1a was linked to promoter regulation as illustrated by its binding to the chromatin around the hypermethylated, inactive rDNA gene promoters. Our data further showed that downregulation of Mybbp1a abrogated the local DNA methylation levels and histone marks associated with gene silencing, and altered the promoter occupancy of various factors such UBF and HDACs, consequently leading to elevated rRNA expression. Mechanistically, we propose that Mybbp1a maintains rDNA repeats in a silenced state while in association with the negative epigenetic modifiers HDAC1/2. CONCLUSIONS Results from our present work reveal a previously unrecognized co-repressor role of Mybbp1a in rRNA expression. They are further consistent with the scenario that Mybbp1a is an integral constituent of the rDNA epigenetic regulation that underlies the balanced state of rDNA clusters.
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Affiliation(s)
- Bertrand Chin-Ming Tan
- Graduate Institute of Biomedical Sciences and Department of Biomedical Sciences, College of Medicine, Chang Gung University, Kwei-San, Tao-Yuan 333, Taiwan
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58
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Shiao YH, Leighty RM, Wang C, Ge X, Crawford EB, Spurrier JM, McCann SD, Fields JR, Fornwald L, Riffle L, Driver C, Kasprzak KS, Quiñones OA, Wilson RE, Travlos GS, Alvord WG, Anderson LM. Molecular and organismal changes in offspring of male mice treated with chemical stressors. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2012; 53:392-407. [PMID: 22674528 DOI: 10.1002/em.21701] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Both gene methylation changes and genetic instability have been noted in offspring of male rodents exposed to radiation or chemicals, but few specific gene targets have been established. Previously, we identified the gene for ribosomal RNA, rDNA, as showing methylation change in sperm of mice treated with the preconceptional carcinogen, chromium(III) chloride. rDNA is a critical cell growth regulator. Here, we investigated the effects of paternal treatments on rDNA in offspring tissue. A total of 93 litters and 758 offspring were obtained, permitting rigorous mixed-effects models statistical analysis of the results. We show that the offspring of male mice treated with Cr(III) presented increased methylation in a promoter sequence of the rDNA gene, specifically in lung. Furthermore polymorphic variants of the multi-copy rDNA genes displayed altered frequencies indicative of structural changes, as a function of both tissue type and paternal treatments. Organismal effects also occurred: some groups of offspring of male mice treated with either Cr(III) or its vehicle, acidic saline, compared with those of untreated mice, had altered average body and liver weights and levels of serum glucose and leptin. Males treated directly with Cr(III) or acidic saline presented serum hormone changes consistent with a stress response. These results establish for the first time epigenetic and genetic instability effects in a gene of central physiological importance, in offspring of male mice exposed preconceptionally to chemicals, possibly related to a stress response in these males.
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Affiliation(s)
- Yih-Horng Shiao
- Laboratory of Comparative Carcinogenesis, Frederick National Laboratory for Cancer Research, Frederick, MD, USA
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59
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Hochstatter J, Hölzel M, Rohrmoser M, Schermelleh L, Leonhardt H, Keough R, Gonda TJ, Imhof A, Eick D, Längst G, Németh A. Myb-binding protein 1a (Mybbp1a) regulates levels and processing of pre-ribosomal RNA. J Biol Chem 2012; 287:24365-77. [PMID: 22645127 DOI: 10.1074/jbc.m111.303719] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Ribosomal RNA gene transcription, co-transcriptional processing, and ribosome biogenesis are highly coordinated processes that are tightly regulated during cell growth. In this study we discovered that Mybbp1a is associated with both the RNA polymerase I complex and the ribosome biogenesis machinery. Using a reporter assay that uncouples transcription and RNA processing, we show that Mybbp1a represses rRNA gene transcription. In addition, overexpression of the protein reduces RNA polymerase I loading on endogenous rRNA genes as revealed by chromatin immunoprecipitation experiments. Accordingly, depletion of Mybbp1a results in an accumulation of the rRNA precursor in vivo but surprisingly also causes growth arrest of the cells. This effect can be explained by the observation that the modulation of Mybbp1a protein levels results in defects in pre-rRNA processing within the cell. Therefore, the protein may play a dual role in the rRNA metabolism, potentially linking and coordinating ribosomal DNA transcription and pre-rRNA processing to allow for the efficient synthesis of ribosomes.
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Affiliation(s)
- Julia Hochstatter
- Biochemistry Center Regensburg, University of Regensburg, Universitätsstrasse 31, 93053 Regensburg, Germany
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60
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Abstract
Over the past 10 years, the development of chromosome conformation capture (3C) technology and the subsequent genomic variants thereof have enabled the analysis of nuclear organization at an unprecedented resolution and throughput. The technology relies on the original and, in hindsight, remarkably simple idea that digestion and religation of fixed chromatin in cells, followed by the quantification of ligation junctions, allows for the determination of DNA contact frequencies and insight into chromosome topology. Here we evaluate and compare the current 3C-based methods (including 4C [chromosome conformation capture-on-chip], 5C [chromosome conformation capture carbon copy], HiC, and ChIA-PET), summarize their contribution to our current understanding of genome structure, and discuss how shape influences genome function.
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Affiliation(s)
- Elzo de Wit
- Hubrecht Institute-KNAW, University Medical Center Utrecht, 3584 CT Utrecht, The Netherlands
| | - Wouter de Laat
- Hubrecht Institute-KNAW, University Medical Center Utrecht, 3584 CT Utrecht, The Netherlands
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61
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Schmolke M, Manicassamy B, Pena L, Sutton T, Hai R, Varga ZT, Hale BG, Steel J, Pérez DR, García-Sastre A. Differential contribution of PB1-F2 to the virulence of highly pathogenic H5N1 influenza A virus in mammalian and avian species. PLoS Pathog 2011; 7:e1002186. [PMID: 21852950 PMCID: PMC3154844 DOI: 10.1371/journal.ppat.1002186] [Citation(s) in RCA: 114] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2011] [Accepted: 06/15/2011] [Indexed: 01/16/2023] Open
Abstract
Highly pathogenic avian influenza A viruses (HPAIV) of the H5N1 subtype occasionally transmit from birds to humans and can cause severe systemic infections in both hosts. PB1-F2 is an alternative translation product of the viral PB1 segment that was initially characterized as a pro-apoptotic mitochondrial viral pathogenicity factor. A full-length PB1-F2 has been present in all human influenza pandemic virus isolates of the 20(th) century, but appears to be lost evolutionarily over time as the new virus establishes itself and circulates in the human host. In contrast, the open reading frame (ORF) for PB1-F2 is exceptionally well-conserved in avian influenza virus isolates. Here we perform a comparative study to show for the first time that PB1-F2 is a pathogenicity determinant for HPAIV (A/Viet Nam/1203/2004, VN1203 (H5N1)) in both mammals and birds. In a mammalian host, the rare N66S polymorphism in PB1-F2 that was previously described to be associated with high lethality of the 1918 influenza A virus showed increased replication and virulence of a recombinant VN1203 H5N1 virus, while deletion of the entire PB1-F2 ORF had negligible effects. Interestingly, the N66S substituted virus efficiently invades the CNS and replicates in the brain of Mx+/+ mice. In ducks deletion of PB1-F2 clearly resulted in delayed onset of clinical symptoms and systemic spreading of virus, while variations at position 66 played only a minor role in pathogenesis. These data implicate PB1-F2 as an important pathogenicity factor in ducks independent of sequence variations at position 66. Our data could explain why PB1-F2 is conserved in avian influenza virus isolates and only impacts pathogenicity in mammals when containing certain amino acid motifs such as the rare N66S polymorphism.
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Affiliation(s)
- Mirco Schmolke
- Department of Microbiology, Mount Sinai School of Medicine, New York, New York, United States of America
| | - Balaji Manicassamy
- Department of Microbiology, Mount Sinai School of Medicine, New York, New York, United States of America
| | - Lindomar Pena
- Department of Veterinary Medicine, University of Maryland, College Park, Maryland, United States of America
| | - Troy Sutton
- Department of Veterinary Medicine, University of Maryland, College Park, Maryland, United States of America
| | - Rong Hai
- Department of Microbiology, Mount Sinai School of Medicine, New York, New York, United States of America
| | - Zsuzsanna T. Varga
- Department of Microbiology, Mount Sinai School of Medicine, New York, New York, United States of America
| | - Benjamin G. Hale
- Department of Microbiology, Mount Sinai School of Medicine, New York, New York, United States of America
| | - John Steel
- Department of Microbiology, Mount Sinai School of Medicine, New York, New York, United States of America
- Department of Microbiology and Immunology, School of Medicine, Emory University, Rollins Research Center, Atlanta, Georgia, United States of America
| | - Daniel R. Pérez
- Department of Veterinary Medicine, University of Maryland, College Park, Maryland, United States of America
| | - Adolfo García-Sastre
- Department of Microbiology, Mount Sinai School of Medicine, New York, New York, United States of America
- Institute of Global Health and Emerging Pathogens, Mount Sinai School of Medicine, New York, New York, United States of America
- Department of Medicine, Mount Sinai School of Medicine, New York, New York, United States of America
- * E-mail:
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Musgrove EA, Sutherland RL. RB in breast cancer: differential effects in estrogen receptor-positive and estrogen receptor-negative disease. Cell Cycle 2011; 9:4607. [PMID: 21260944 DOI: 10.4161/cc.9.23.13889] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
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63
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Németh A, Längst G. Genome organization in and around the nucleolus. Trends Genet 2011; 27:149-56. [DOI: 10.1016/j.tig.2011.01.002] [Citation(s) in RCA: 130] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2010] [Revised: 01/03/2011] [Accepted: 01/04/2011] [Indexed: 10/18/2022]
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64
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Denissov S, Lessard F, Mayer C, Stefanovsky V, van Driel M, Grummt I, Moss T, Stunnenberg HG. A model for the topology of active ribosomal RNA genes. EMBO Rep 2011; 12:231-7. [PMID: 21331097 DOI: 10.1038/embor.2011.8] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2010] [Revised: 01/10/2011] [Accepted: 01/13/2011] [Indexed: 01/03/2023] Open
Abstract
The Christmas tree view of active ribosomal RNA (rRNA) genes suggests a gene topology in which a large number of nascent rRNA transcripts are prevented from intertwining. The way in which this is achieved has remained unclear. By using a combination of chromatin immunoprecipitation and chromosome conformation capture techniques, we show that the promoter, upstream region and terminator R3 of active rRNA genes are held together spatially throughout the cell cycle, forming a stable core around which the transcribed region is organized. We suggest a new core-helix model for the topology of rRNA genes, that provides a structural basis for the productive synthesis or rRNA.
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Affiliation(s)
- Serguei Denissov
- Science Faculty, Department of Molecular Biology, Nijmegen Centre for Molecular Life Sciences, Radboud University (274), PO Box 9101, Nijmegen 6500 HB, The Netherlands
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65
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Poortinga G, Wall M, Sanij E, Siwicki K, Ellul J, Brown D, Holloway TP, Hannan RD, McArthur GA. c-MYC coordinately regulates ribosomal gene chromatin remodeling and Pol I availability during granulocyte differentiation. Nucleic Acids Res 2010; 39:3267-81. [PMID: 21177653 PMCID: PMC3082905 DOI: 10.1093/nar/gkq1205] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Loss of c-MYC is required for downregulation of ribosomal RNA (rRNA) gene (rDNA) transcription by RNA Polymerase I (Pol I) during granulocyte differentiation. Here, we demonstrate a robust reduction of Pol I loading onto rDNA that along with a depletion of the MYC target gene upstream binding factor (UBF) and a switch from epigenetically active to silent rDNA accompanies this MYC reduction. We hypothesized that MYC may coordinate these mechanisms via direct regulation of multiple components of the Pol I transcription apparatus. Using gene expression arrays we identified a ‘regulon’ of Pol I factors that are both downregulated during differentiation and reinduced in differentiated granulocytes upon activation of the MYC-ER transgene. This regulon includes the novel c-MYC target genes RRN3 and POLR1B. Although enforced MYC expression during granulocyte differentiation was sufficient to increase the number of active rRNA genes, its activation in terminally differentiated cells did not alter the active to inactive gene ratio despite increased rDNA transcription. Thus, c-MYC dynamically controls rDNA transcription during granulocytic differentiation through the orchestrated transcriptional regulation of core Pol I factors and epigenetic modulation of number of active rRNA genes.
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Affiliation(s)
- Gretchen Poortinga
- Division of Research, Peter MacCallum Cancer Centre, St Andrews Place, East Melbourne, Victoria, Australia.
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van de Nobelen S, Rosa-Garrido M, Leers J, Heath H, Soochit W, Joosen L, Jonkers I, Demmers J, van der Reijden M, Torrano V, Grosveld F, Delgado MD, Renkawitz R, Galjart N, Sleutels F. CTCF regulates the local epigenetic state of ribosomal DNA repeats. Epigenetics Chromatin 2010; 3:19. [PMID: 21059229 PMCID: PMC2993708 DOI: 10.1186/1756-8935-3-19] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2010] [Accepted: 11/08/2010] [Indexed: 02/06/2023] Open
Abstract
Background CCCTC binding factor (CTCF) is a highly conserved zinc finger protein, which is involved in chromatin organization, local histone modifications, and RNA polymerase II-mediated gene transcription. CTCF may act by binding tightly to DNA and recruiting other proteins to mediate its various functions in the nucleus. To further explore the role of this essential factor, we used a mass spectrometry-based approach to screen for novel CTCF-interacting partners. Results Using biotinylated CTCF as bait, we identified upstream binding factor (UBF) and multiple other components of the RNA polymerase I complex as potential CTCF-interacting partners. Interestingly, CTCFL, the testis-specific paralog of CTCF, also binds UBF. The interaction between CTCF(L) and UBF is direct, and requires the zinc finger domain of CTCF(L) and the high mobility group (HMG)-box 1 and dimerization domain of UBF. Because UBF is involved in RNA polymerase I-mediated ribosomal (r)RNA transcription, we analyzed CTCF binding to the rDNA repeat. We found that CTCF bound to a site upstream of the rDNA spacer promoter and preferred non-methylated over methylated rDNA. DNA binding by CTCF in turn stimulated binding of UBF. Absence of CTCF in cultured cells resulted in decreased association of UBF with rDNA and in nucleolar fusion. Furthermore, lack of CTCF led to reduced binding of RNA polymerase I and variant histone H2A.Z near the rDNA spacer promoter, a loss of specific histone modifications, and diminished transcription of non-coding RNA from the spacer promoter. Conclusions UBF is the first common interaction partner of CTCF and CTCFL, suggesting a role for these proteins in chromatin organization of the rDNA repeats. We propose that CTCF affects RNA polymerase I-mediated events globally by controlling nucleolar number, and locally by regulating chromatin at the rDNA spacer promoter, similar to RNA polymerase II promoters. CTCF may load UBF onto rDNA, thereby forming part of a network that maintains rDNA genes poised for transcription.
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67
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Singh SK, Sabatinos S, Forsburg S, Bastia D. Regulation of replication termination by Reb1 protein-mediated action at a distance. Cell 2010; 142:868-78. [PMID: 20850009 DOI: 10.1016/j.cell.2010.08.013] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2010] [Revised: 06/08/2010] [Accepted: 07/26/2010] [Indexed: 11/30/2022]
Abstract
DNA transactions driven by long-range protein-mediated inter- and intrachromosomal interactions have been reported to influence gene expression. Here, we report that site-specific replication termination in Schizosaccharomyces pombe is modulated by protein-mediated interactions between pairs of Ter sites located either on the same or on different chromosomes. The dimeric Reb1 protein catalyzes termination and mediates interaction between Ter sites. The Reb1-dependent interactions between two antiparallel Ter sites in cis caused looping out of the intervening DNA in vitro and enhancement of fork arrest in vivo. A Ter site on chromosome 2 interacted pairwise with two Ter sites located on chromosome 1 by chromosome kissing. Mutational inactivation of the major interacting Ter site on chromosome 1 significantly reduced fork arrest at the Ter site on chromosome 2, thereby revealing a cooperative mechanism of control of replication termination.
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Affiliation(s)
- Samarendra K Singh
- Department of Molecular Biology and Biochemistry, Medical University of South Carolina, Charleston, SC 29425, USA
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68
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Dicer is associated with ribosomal DNA chromatin in mammalian cells. PLoS One 2010; 5:e12175. [PMID: 20730047 PMCID: PMC2921364 DOI: 10.1371/journal.pone.0012175] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2010] [Accepted: 07/10/2010] [Indexed: 01/18/2023] Open
Abstract
Background RNA silencing is a common term for pathways utilizing small RNAs as sequence-specific guides to repress gene expression. Components of the RNA silencing machinery are involved in different aspects of chromatin function in numerous organisms. However, association of RNA silencing with chromatin in mammalian cells remains unclear. Methodology/Principal Findings Immunostaining of mitotic chromosomes with antibodies visualizing either endogenous or ectopically expressed Dicer in mammalian cells revealed association of the protein with ribosomal DNA (rDNA) repeats. Chromatin immunoprecipitations and bisulfite sequencing experiments indicated that Dicer is associated with transcribed regions of both active and silenced genes in rDNA arrays of interphase chromosomes. Metabolic labeling of the mouse embryonic stem (ES) cells lacking Dicer did not reveal apparent defect in rRNA biogenesis though pre-rRNA synthesis in these cells was decreased, likely as a consequence of their slower growth caused by the loss of miRNAs. We analyzed in detail chromatin structure of rDNA but did not find any epigenetic changes at rDNA loci in Dicer−/− ES cells. Instead, we found that rDNA methylation is rather low in primary tissues, contrasting with rDNA methylation patterns in transformed cell lines. Conclusion/Significance We found that Dicer, a key component of RNA silencing pathways, can be detected in association with rDNA chromatin in mammalian cells. The role of this particular localization of Dicer is not readily apparent since the enzyme is associated with rDNA genes regardless of their transcriptional activity. However, localization of Dicer to the transcribed region suggests that transcription may contribute to the Dicer deposition at rDNA chromatin. We hypothesize that Dicer functions in maintaining integrity of rDNA arrays.
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69
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Felle M, Exler JH, Merkl R, Dachauer K, Brehm A, Grummt I, Längst G. DNA sequence encoded repression of rRNA gene transcription in chromatin. Nucleic Acids Res 2010; 38:5304-14. [PMID: 20421213 PMCID: PMC2938192 DOI: 10.1093/nar/gkq263] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Eukaryotic genomes are packaged into nucleosomes that occlude DNA from interacting with most DNA-binding proteins. Nucleosome positioning and chromatin organization is critical for gene regulation. We have investigated the mechanism by which nucleosomes are positioned at the promoters of active and silent rRNA genes (rDNA). The reconstitution of nucleosomes on rDNA results in sequence-dependent nucleosome positioning at the rDNA promoter that mimics the chromatin structure of silent rRNA genes in vivo, suggesting that active mechanisms are required to reorganize chromatin structure upon gene activation. Nucleosomes are excluded from positions observed at active rRNA genes, resulting in transcriptional repression on chromatin. We suggest that the repressed state is the default chromatin organization of the rDNA and gene activation requires ATP-dependent chromatin remodelling activities that move the promoter-bound nucleosome about 22-bp upstream. We suggest that nucleosome remodelling precedes promoter-dependent transcriptional activation as specific inhibition of ATP-dependent chromatin remodelling suppresses the initiation of RNA Polymerase I transcription in vitro. Once initiated, RNA Polymerase I is capable of elongating through reconstituted chromatin without apparent displacement of the nucleosomes. The results reveal the functional cooperation of DNA sequence and chromatin remodelling complexes in nucleosome positioning and in establishing the epigenetic active or silent state of rRNA genes.
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Affiliation(s)
- Max Felle
- Institut für Biochemie III, Universität Regensburg, Universitätsstr. 31, 93053 Regensburg, Germany
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70
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Abstract
The genome forms extensive and dynamic physical interactions with itself in the form of chromosome loops and bridges, thus exploring the three-dimensional space of the nucleus. It is now possible to examine these interactions at the molecular level, and we have gained glimpses of their functional implications. Chromosomal interactions can contribute to the silencing and activation of genes within the three-dimensional context of the nuclear architecture. Technical advances in detecting these interactions contribute to our understanding of the functional organization of the genome, as well as its adaptive plasticity in response to environmental changes during development and disease.
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Affiliation(s)
- Anita Göndör
- Department of Microbiology, Tumor and Cell Biology, Nobels väg 16, Box 280, Karolinska Institute, SE-171 77 Stockholm, Sweden.
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71
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Shiue CN, Berkson RG, Wright APH. c-Myc induces changes in higher order rDNA structure on stimulation of quiescent cells. Oncogene 2009; 28:1833-42. [PMID: 19270725 DOI: 10.1038/onc.2009.21] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
c-Myc is an oncogenic transcription factor capable of activating transcription by all three nuclear RNA polymerases, thus acting as a high-level coordinator of protein synthesis capacity and cell growth rate. c-Myc recruits RNA polymerase I-related transcription factors to the rDNA when quiescent cells are stimulated to re-enter the cell cycle. Using a model system of cell lines with variable c-Myc status, we show that on stimulation c-Myc rapidly induces gene loop structures in rDNA chromatin that juxtapose upstream and downstream rDNA sequences. c-Myc activation is both necessary and sufficient for this change in rDNA chromatin conformation. c-Myc activation induces association of TTF-1 with the rDNA, and c-Myc is physically associated with induced rDNA gene loops. The origins of two or more rDNA gene loops are closely juxtaposed, suggesting the possibility that c-Myc induces nucleolar chromatin hubs. Induction of rDNA gene loops may be an early step in the reprogramming of quiescent cells as they re-enter the growth cycle.
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Affiliation(s)
- C-N Shiue
- Södertörns Högskola and Department of Biosciences and Nutrition, Karolinska Institutet, Huddinge, Sweden
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72
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Birch JL, Tan BCM, Panov KI, Panova TB, Andersen JS, Owen-Hughes TA, Russell J, Lee SC, Zomerdijk JCBM. FACT facilitates chromatin transcription by RNA polymerases I and III. EMBO J 2009; 28:854-65. [PMID: 19214185 PMCID: PMC2647773 DOI: 10.1038/emboj.2009.33] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2008] [Accepted: 01/21/2009] [Indexed: 01/23/2023] Open
Abstract
Efficient transcription elongation from a chromatin template requires RNA polymerases (Pols) to negotiate nucleosomes. Our biochemical analyses demonstrate that RNA Pol I can transcribe through nucleosome templates and that this requires structural rearrangement of the nucleosomal core particle. The subunits of the histone chaperone FACT (facilitates chromatin transcription), SSRP1 and Spt16, co-purify and co-immunoprecipitate with mammalian Pol I complexes. In cells, SSRP1 is detectable at the rRNA gene repeats. Crucially, siRNA-mediated repression of FACT subunit expression in cells results in a significant reduction in 47S pre-rRNA levels, whereas synthesis of the first 40 nt of the rRNA is not affected, implying that FACT is important for Pol I transcription elongation through chromatin. FACT also associates with RNA Pol III complexes, is present at the chromatin of genes transcribed by Pol III and facilitates their transcription in cells. Our findings indicate that, beyond the established role in Pol II transcription, FACT has physiological functions in chromatin transcription by all three nuclear RNA Pols. Our data also imply that local chromatin dynamics influence transcription of the active rRNA genes by Pol I and of Pol III-transcribed genes.
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Affiliation(s)
- Joanna L Birch
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee, UK
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73
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Abstract
Transcription of the major ribosomal RNAs by Pol I (RNA polymerase I) is a key determinant of ribosome biogenesis, driving cell growth and proliferation in eukaryotes. Hundreds of copies of rRNA genes are present in each cell, and there is evidence that the cellular control of Pol I transcription involves adjustments to the number of rRNA genes actively engaged in transcription, as well as to the rate of transcription from each active gene. Chromatin structure is inextricably linked to rRNA gene activity, and the present review highlights recent advances in this area.
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Affiliation(s)
- Joanna L. Birch
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee DD1 5EH, U.K
| | - Joost C.B.M. Zomerdijk
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee DD1 5EH, U.K
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Kawauchi J, Mischo H, Braglia P, Rondon A, Proudfoot NJ. Budding yeast RNA polymerases I and II employ parallel mechanisms of transcriptional termination. Genes Dev 2008; 22:1082-92. [PMID: 18413718 DOI: 10.1101/gad.463408] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Both RNA polymerase I and II (Pol I and Pol II) in budding yeast employ a functionally homologous "torpedo-like" mechanism to promote transcriptional termination. For two well-defined Pol II-transcribed genes, CYC1 and PMA1, we demonstrate that both Rat1p exonuclease and Sen1p helicase are required for efficient termination by promoting degradation of the nascent transcript associated with Pol II, following mRNA 3' end processing. Similarly, Pol I termination relies on prior Rnt1p cleavage at the 3' end of the pre-rRNA 35S transcript. This is followed by the combined actions of Rat1p and Sen1p to degrade the Pol I-associated nascent transcript that consequently promote termination in the downstream rDNA spacer sequence. Our data suggest that the previously defined in vitro Pol I termination mechanism involving the action of the Reb1p DNA-binding factor to "road-block" Pol I transcription close to the termination region may have overlooked more complex in vivo molecular processes.
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Affiliation(s)
- Junya Kawauchi
- Sir William Dunn School of Pathology, Oxford OX1 3RE, United Kingdom
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