1
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Pelea O, Fulga TA, Sauka-Spengler T. RNA-Responsive gRNAs for Controlling CRISPR Activity: Current Advances, Future Directions, and Potential Applications. CRISPR J 2022; 5:642-659. [PMID: 36206027 PMCID: PMC9618385 DOI: 10.1089/crispr.2022.0052] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
CRISPR-Cas9 has emerged as a major genome manipulation tool. As Cas9 can cause off-target effects, several methods for controlling the expression of CRISPR systems were developed. Recent studies have shown that CRISPR activity could be controlled by sensing expression levels of endogenous transcripts. This is particularly interesting, as endogenous RNAs could harbor important information about the cell type, disease state, and environmental challenges cells are facing. Single-guide RNA (sgRNA) engineering played a major role in the development of RNA-responsive CRISPR systems. Following further optimizations, RNA-responsive sgRNAs could enable the development of novel therapeutic and research applications. This review introduces engineering strategies that could be employed to modify Streptococcus pyogenes sgRNAs with a focus on recent advances made toward the development of RNA-responsive sgRNAs. Future directions and potential applications of these technologies are also discussed.
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Affiliation(s)
- Oana Pelea
- Radcliffe Department of Medicine, MRC Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, United Kingdom; and Kansas City, Missouri, USA.,Address correspondence to: Oana Pelea, Radcliffe Department of Medicine, MRC Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, United Kingdom,
| | - Tudor A. Fulga
- Radcliffe Department of Medicine, MRC Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, United Kingdom; and Kansas City, Missouri, USA
| | - Tatjana Sauka-Spengler
- Radcliffe Department of Medicine, MRC Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, United Kingdom; and Kansas City, Missouri, USA.,Stowers Institute for Medical Research, Kansas City, Missouri, USA.,Address correspondence to: Tatjana Sauka-Spengler, Radcliffe Department of Medicine, MRC Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, United Kingdom,
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2
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Hieronymus R, Zhu J, Müller S. RNA self-splicing by engineered hairpin ribozyme variants. Nucleic Acids Res 2021; 50:368-377. [PMID: 34928378 PMCID: PMC8754997 DOI: 10.1093/nar/gkab1239] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2021] [Revised: 11/26/2021] [Accepted: 12/03/2021] [Indexed: 11/14/2022] Open
Abstract
Small RNAs capable of self-cleavage and ligation might have been the precursors for the much more complex self-splicing group I and II introns in an early RNA world. Here, we demonstrate the activity of engineered hairpin ribozyme variants, which as self-splicing introns are removed from their parent RNA. In the process, two cleavage reactions are supported at the two intron-exon junctions, followed by ligation of the two generated exon fragments. As a result, the hairpin ribozyme, here acting as the self-splicing intron, is cut out. Two self-splicing hairpin ribozyme variants were investigated, one designed by hand, the other by a computer-aided approach. Both variants perform self-splicing, generating a cut-out intron and ligated exons.
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Affiliation(s)
- Robert Hieronymus
- Institute of Biochemistry, University of Greifswald, Felix-Hausdorff-Str. 4, 17487 Greifswald, Germany
| | - Jikang Zhu
- Institute of Biochemistry, University of Greifswald, Felix-Hausdorff-Str. 4, 17487 Greifswald, Germany
| | - Sabine Müller
- Institute of Biochemistry, University of Greifswald, Felix-Hausdorff-Str. 4, 17487 Greifswald, Germany
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3
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Abstract
To exert their functions, RNAs adopt diverse structures, ranging from simple secondary to complex tertiary and quaternary folds. In vivo, RNA folding starts with RNA transcription, and a wide variety of processes are coupled to co-transcriptional RNA folding events, including the regulation of fundamental transcription dynamics, gene regulation by mechanisms like attenuation, RNA processing or ribonucleoprotein particle formation. While co-transcriptional RNA folding and associated co-transcriptional processes are by now well accepted as pervasive regulatory principles in all organisms, investigations into the role of the transcription machinery in co-transcriptional folding processes have so far largely focused on effects of the order in which RNA regions are produced and of transcription kinetics. Recent structural and structure-guided functional analyses of bacterial transcription complexes increasingly point to an additional role of RNA polymerase and associated transcription factors in supporting co-transcriptional RNA folding by fostering or preventing strategic contacts to the nascent transcripts. In general, the results support the view that transcription complexes can act as RNA chaperones, a function that has been suggested over 30 years ago. Here, we discuss transcription complexes as RNA chaperones based on recent examples from bacterial transcription.
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Affiliation(s)
- Nelly Said
- Freie Universität Berlin, Department Biology, Chemistry, Pharmacy, Institute of Chemistry and Biochemistry, Laboratory of Structural Biochemistry, Berlin, Germany
| | - Markus C Wahl
- Freie Universität Berlin, Department Biology, Chemistry, Pharmacy, Institute of Chemistry and Biochemistry, Laboratory of Structural Biochemistry, Berlin, Germany.,Helmholtz-Zentrum Berlin Für Materialien Und Energie, Macromolecular Crystallography, Berlin, Germany
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4
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Armaleo D, Chiou L. Modeling in yeast how rDNA introns slow growth and increase desiccation tolerance in lichens. G3 GENES|GENOMES|GENETICS 2021; 11:6347584. [PMID: 34849787 PMCID: PMC8527467 DOI: 10.1093/g3journal/jkab279] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/03/2021] [Accepted: 07/16/2021] [Indexed: 11/13/2022]
Abstract
Abstract
We connect ribosome biogenesis to desiccation tolerance in lichens, widespread symbioses between specialized fungi (mycobionts) and unicellular phototrophs. We test whether the introns present in the nuclear ribosomal DNA of lichen mycobionts contribute to their anhydrobiosis. Self-splicing introns are found in the rDNA of several eukaryotic microorganisms, but most introns populating lichen rDNA are unable to self-splice, being either catalytically impaired group I introns, or spliceosomal introns ectopically present in rDNA. Although the mycobiont’s splicing machinery removes all introns from rRNA, Northern analysis indicates delayed post-transcriptional removal during rRNA processing, suggesting interference with ribosome assembly. To study the effects of lichen introns in a model system, we used CRISPR to introduce a spliceosomal rDNA intron from the lichen fungus Cladonia grayi into all nuclear rDNA copies of Saccharomyces cerevisiae, which lacks rDNA introns. Three intron-bearing yeast mutants were constructed with the intron inserted either in the 18S rRNA genes, the 25S rRNA genes, or in both. The mutants removed the introns correctly but had half the rDNA genes of the wildtype, grew 4.4–6 times slower, and were 40–1700 times more desiccation tolerant depending on intron position and number. Intracellular trehalose, a disaccharide implicated in desiccation tolerance, was detected at low concentration. Our data suggest that the interference of the splicing machinery with ribosome assembly leads to fewer ribosomes and proteins and to slow growth and increased desiccation tolerance in the yeast mutants. The relevance of these findings for slow growth and desiccation tolerance in lichens is discussed.
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Affiliation(s)
- Daniele Armaleo
- Department of Biology, Duke University, Durham, NC 27708, USA
| | - Lilly Chiou
- Department of Biology, Duke University, Durham, NC 27708, USA
- Curriculum in Genetics and Molecular Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
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5
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Bokolia NP, Khan IA. Regulation of polyphosphate glucokinase gene expression through co-transcriptional processing in Mycobacterium tuberculosis H37Rv. J Biochem 2021; 170:593-609. [PMID: 34247237 DOI: 10.1093/jb/mvab080] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2021] [Accepted: 07/01/2021] [Indexed: 11/14/2022] Open
Abstract
Transcription is a molecular process that involves the synthesis of RNA chain into the 5'-3' direction, and simultaneously nascent RNA chain tends to form geometric structures, known as co-transcriptional folding. This folding determines the functional properties of RNA molecules and possibly has a critical role during the synthesis. This functioning includes the characterized properties of riboswitches and ribozymes, which are significant when the transcription rate is comparable to the cellular environment. This study reports a novel non-coding region important in the genetic expression of polyphosphate glucokinase (ppgk) in Mycobacterium tuberculosis. This non-coding element of ppgk gene undergoes cleavage activity during the transcriptional process in Mycobacterium tuberculosis. We revealed that cleavage occurs within the nascent RNA, and the resultant cleaved 3'RNA fragment carries the Shine- Dalgarno (SD) sequence and expression platform. We concluded co-transcriptional processing at the non-coding region as the required mechanism for ppgk expression that remains constitutive within the bacterial environment. This study defines the molecular mechanism dependent on the transient but highly active structural features of the nascent RNA.
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Affiliation(s)
- Naveen Prakash Bokolia
- Clinical Microbiology Division, CSIR-Indian Institute of Integrative Medicine, Jammu 180001, India.,Academy of Scientific and Innovative Research (AcSIR), Ghaziabad- 201002, India
| | - Inshad Ali Khan
- Department of Microbiology, Central University of Rajasthan, Bandarsindri, Ajmer, 305817, India
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6
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Schärfen L, Neugebauer KM. Transcription Regulation Through Nascent RNA Folding. J Mol Biol 2021; 433:166975. [PMID: 33811916 DOI: 10.1016/j.jmb.2021.166975] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2021] [Revised: 03/23/2021] [Accepted: 03/24/2021] [Indexed: 12/14/2022]
Abstract
Folding of RNA into secondary structures through intramolecular base pairing determines an RNA's three-dimensional architecture and associated function. Simple RNA structures like stem loops can provide specialized functions independent of coding capacity, such as protein binding, regulation of RNA processing and stability, stimulation or inhibition of translation. RNA catalysis is dependent on tertiary structures found in the ribosome, tRNAs and group I and II introns. While the extent to which non-coding RNAs contribute to cellular maintenance is generally appreciated, the fact that both non-coding and coding RNA can assume relevant structural states has only recently gained attention. In particular, the co-transcriptional folding of nascent RNA of all classes has the potential to regulate co-transcriptional processing, RNP (ribonucleoprotein particle) formation, and transcription itself. Riboswitches are established examples of co-transcriptionally folded coding RNAs that directly regulate transcription, mainly in prokaryotes. Here we discuss recent studies in both prokaryotes and eukaryotes showing that structure formation may carry a more widespread regulatory logic during RNA synthesis. Local structures forming close to the catalytic center of RNA polymerases have the potential to regulate transcription by reducing backtracking. In addition, stem loops or more complex structures may alter co-transcriptional RNA processing or its efficiency. Several examples of functional structures have been identified to date, and this review provides an overview of physiologically distinct processes where co-transcriptionally folded RNA plays a role. Experimental approaches such as single-molecule FRET and in vivo structural probing to further advance our insight into the significance of co-transcriptional structure formation are discussed.
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Affiliation(s)
- Leonard Schärfen
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
| | - Karla M Neugebauer
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA.
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7
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Jarmoskaite I, Tijerina P, Russell R. ATP utilization by a DEAD-box protein during refolding of a misfolded group I intron ribozyme. J Biol Chem 2020; 296:100132. [PMID: 33262215 PMCID: PMC7948464 DOI: 10.1074/jbc.ra120.015029] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2020] [Revised: 11/17/2020] [Accepted: 12/01/2020] [Indexed: 12/31/2022] Open
Abstract
DEAD-box helicase proteins perform ATP-dependent rearrangements of structured RNAs throughout RNA biology. Short RNA helices are unwound in a single ATPase cycle, but the ATP requirement for more complex RNA structural rearrangements is unknown. Here we measure the amount of ATP used for native refolding of a misfolded group I intron ribozyme by CYT-19, a Neurospora crassa DEAD-box protein that functions as a general chaperone for mitochondrial group I introns. By comparing the rates of ATP hydrolysis and ribozyme refolding, we find that several hundred ATP molecules are hydrolyzed during refolding of each ribozyme molecule. After subtracting nonproductive ATP hydrolysis that occurs in the absence of ribozyme refolding, we find that approximately 100 ATPs are hydrolyzed per refolded RNA as a consequence of interactions specific to the misfolded ribozyme. This value is insensitive to changes in ATP and CYT-19 concentration and decreases with decreasing ribozyme stability. Because of earlier findings that ∼90% of global ribozyme unfolding cycles lead back to the kinetically preferred misfolded conformation and are not observed, we estimate that each global unfolding cycle consumes ∼10 ATPs. Our results indicate that CYT-19 functions as a general RNA chaperone by using a stochastic, energy-intensive mechanism to promote RNA unfolding and refolding, suggesting an evolutionary convergence with protein chaperones.
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Affiliation(s)
- Inga Jarmoskaite
- Department of Molecular Biosciences, University of Texas at Austin, Austin, Texas, USA
| | - Pilar Tijerina
- Department of Molecular Biosciences, University of Texas at Austin, Austin, Texas, USA
| | - Rick Russell
- Department of Molecular Biosciences, University of Texas at Austin, Austin, Texas, USA.
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8
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Wang Y, Wang Z, Liu T, Gong S, Zhang W. Effects of flanking regions on HDV cotranscriptional folding kinetics. RNA (NEW YORK, N.Y.) 2018; 24:1229-1240. [PMID: 29954950 PMCID: PMC6097654 DOI: 10.1261/rna.065961.118] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/06/2018] [Accepted: 06/25/2018] [Indexed: 05/20/2023]
Abstract
Hepatitis delta virus (HDV) ribozyme performs the self-cleavage activity through folding to a double pseudoknot structure. The folding of functional RNA structures is often coupled with the transcription process. In this work, we developed a new approach for predicting the cotranscriptional folding kinetics of RNA secondary structures with pseudoknots. We theoretically studied the cotranscriptional folding behavior of the 99-nucleotide (nt) HDV sequence, two upstream flanking sequences, and one downstream flanking sequence. During transcription, the 99-nt HDV can effectively avoid the trap intermediates and quickly fold to the cleavage-active state. It is different from its refolding kinetics, which folds into an intermediate trap state. For all the sequences, the ribozyme regions (from 1 to 73) all fold to the same structure during transcription. However, the existence of the 30-nt upstream flanking sequence can inhibit the ribozyme region folding into the active native state through forming an alternative helix Alt1 with the segments 70-90. The longer upstream flanking sequence of 54 nt itself forms a stable hairpin structure, which sequesters the formation of the Alt1 helix and leads to rapid formation of the cleavage-active structure. Although the 55-nt downstream flanking sequence could invade the already folded active structure during transcription by forming a more stable helix with the ribozyme region, the slow transition rate could keep the structure in the cleavage-active structure to perform the activity.
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Affiliation(s)
- Yanli Wang
- Department of Physics, Wuhan University, Wuhan, Hubei 430072, P.R. China
| | - Zhen Wang
- Department of Physics, Wuhan University, Wuhan, Hubei 430072, P.R. China
| | - Taigang Liu
- Department of Physics, Wuhan University, Wuhan, Hubei 430072, P.R. China
| | - Sha Gong
- Department of Physics, Wuhan University, Wuhan, Hubei 430072, P.R. China
| | - Wenbing Zhang
- Department of Physics, Wuhan University, Wuhan, Hubei 430072, P.R. China
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9
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Piao M, Sun L, Zhang QC. RNA Regulations and Functions Decoded by Transcriptome-wide RNA Structure Probing. GENOMICS PROTEOMICS & BIOINFORMATICS 2017; 15:267-278. [PMID: 29031843 PMCID: PMC5673676 DOI: 10.1016/j.gpb.2017.05.002] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/27/2017] [Revised: 05/09/2017] [Accepted: 05/27/2017] [Indexed: 01/07/2023]
Abstract
RNA folds into intricate structures that are crucial for its functions and regulations. To date, a multitude of approaches for probing structures of the whole transcriptome, i.e., RNA structuromes, have been developed. Applications of these approaches to different cell lines and tissues have generated a rich resource for the study of RNA structure–function relationships at a systems biology level. In this review, we first introduce the designs of these methods and their applications to study different RNA structuromes. We emphasize their technological differences especially their unique advantages and caveats. We then summarize the structural insights in RNA functions and regulations obtained from the studies of RNA structuromes. And finally, we propose potential directions for future improvements and studies.
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Affiliation(s)
- Meiling Piao
- MOE Key Laboratory of Bioinformatics, Beijing Advanced Innovation Center for Structural Biology, Center for Synthetic and Systems Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Lei Sun
- MOE Key Laboratory of Bioinformatics, Beijing Advanced Innovation Center for Structural Biology, Center for Synthetic and Systems Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Qiangfeng Cliff Zhang
- MOE Key Laboratory of Bioinformatics, Beijing Advanced Innovation Center for Structural Biology, Center for Synthetic and Systems Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China.
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10
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Meyer IM. In silico methods for co-transcriptional RNA secondary structure prediction and for investigating alternative RNA structure expression. Methods 2017; 120:3-16. [PMID: 28433606 DOI: 10.1016/j.ymeth.2017.04.009] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2017] [Revised: 03/16/2017] [Accepted: 04/14/2017] [Indexed: 01/26/2023] Open
Abstract
RNA transcripts are the primary products of active genes in any living organism, including many viruses. Their cellular destiny not only depends on primary sequence signals, but can also be determined by RNA structure. Recent experimental evidence shows that many transcripts can be assigned more than a single functional RNA structure throughout their cellular life and that structure formation happens co-transcriptionally, i.e. as the transcript is synthesised in the cell. Moreover, functional RNA structures are not limited to non-coding transcripts, but can also feature in coding transcripts. The picture that now emerges is that RNA structures constitute an additional layer of information that can be encoded in any RNA transcript (and on top of other layers of information such as protein-context) in order to exert a wide range of functional roles. Moreover, different encoded RNA structures can be expressed at different stages of a transcript's life in order to alter the transcript's behaviour depending on its actual cellular context. Similar to the concept of alternative splicing for protein-coding genes, where a single transcript can yield different proteins depending on cellular context, it is thus appropriate to propose the notion of alternative RNA structure expression for any given transcript. This review introduces several computational strategies that my group developed to detect different aspects of RNA structure expression in vivo. Two aspects are of particular interest to us: (1) RNA secondary structure features that emerge during co-transcriptional folding and (2) functional RNA structure features that are expressed at different times of a transcript's life and potentially mutually exclusive.
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Affiliation(s)
- Irmtraud M Meyer
- Laboratory of Bioinformatics of RNA Structure and Transcriptome Regulation, Berlin Institute for Medical Systems Biology, Max Delbrück Center for Molecular Medicine, Robert-Rössle-Str. 10, 13125 Berlin-Buch, Germany; Institute of Chemistry and Biochemistry, Free University, Thielallee 63, 14195 Berlin, Germany.
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11
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Helmling C, Wacker A, Wolfinger MT, Hofacker IL, Hengesbach M, Fürtig B, Schwalbe H. NMR Structural Profiling of Transcriptional Intermediates Reveals Riboswitch Regulation by Metastable RNA Conformations. J Am Chem Soc 2017; 139:2647-2656. [PMID: 28134517 DOI: 10.1021/jacs.6b10429] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Gene repression induced by the formation of transcriptional terminators represents a prime example for the coupling of RNA synthesis, folding, and regulation. In this context, mapping the changes in available conformational space of transcription intermediates during RNA synthesis is important to understand riboswitch function. A majority of riboswitches, an important class of small metabolite-sensing regulatory RNAs, act as transcriptional regulators, but the dependence of ligand binding and the subsequent allosteric conformational switch on mRNA transcript length has not yet been investigated. We show a strict fine-tuning of binding and sequence-dependent alterations of conformational space by structural analysis of all relevant transcription intermediates at single-nucleotide resolution for the I-A type 2'dG-sensing riboswitch from Mesoplasma florum by NMR spectroscopy. Our results provide a general framework to dissect the coupling of synthesis and folding essential for riboswitch function, revealing the importance of metastable states for RNA-based gene regulation.
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Affiliation(s)
- Christina Helmling
- Institute for Organic Chemisty and Chemical Biology, Center for Biomolecular Magnetic Resonance (BMRZ), Johann Wolfgang Goethe-Universität , Frankfurt/M. 60438, Germany
| | - Anna Wacker
- Institute for Organic Chemisty and Chemical Biology, Center for Biomolecular Magnetic Resonance (BMRZ), Johann Wolfgang Goethe-Universität , Frankfurt/M. 60438, Germany
| | - Michael T Wolfinger
- Medical University of Vienna , Center for Anatomy and Cell Biology, Währingerstraße 13, 1090 Vienna, Austria
| | | | - Martin Hengesbach
- Institute for Organic Chemisty and Chemical Biology, Center for Biomolecular Magnetic Resonance (BMRZ), Johann Wolfgang Goethe-Universität , Frankfurt/M. 60438, Germany
| | - Boris Fürtig
- Institute for Organic Chemisty and Chemical Biology, Center for Biomolecular Magnetic Resonance (BMRZ), Johann Wolfgang Goethe-Universität , Frankfurt/M. 60438, Germany
| | - Harald Schwalbe
- Institute for Organic Chemisty and Chemical Biology, Center for Biomolecular Magnetic Resonance (BMRZ), Johann Wolfgang Goethe-Universität , Frankfurt/M. 60438, Germany
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12
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Andersen KL, Beckert B, Masquida B, Johansen SD, Nielsen H. Accumulation of Stable Full-Length Circular Group I Intron RNAs during Heat-Shock. Molecules 2016; 21:molecules21111451. [PMID: 27809244 PMCID: PMC6274462 DOI: 10.3390/molecules21111451] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2016] [Revised: 10/25/2016] [Accepted: 10/27/2016] [Indexed: 02/07/2023] Open
Abstract
Group I introns in nuclear ribosomal RNA of eukaryotic microorganisms are processed by splicing or circularization. The latter results in formation of full-length circular introns without ligation of the exons and has been proposed to be active in intron mobility. We applied qRT-PCR to estimate the copy number of circular intron RNA from the myxomycete Didymium iridis. In exponentially growing amoebae, the circular introns are nuclear and found in 70 copies per cell. During heat-shock, the circular form is up-regulated to more than 500 copies per cell. The intron harbours two ribozymes that have the potential to linearize the circle. To understand the structural features that maintain circle integrity, we performed chemical and enzymatic probing of the splicing ribozyme combined with molecular modeling to arrive at models of the inactive circular form and its active linear counterpart. We show that the two forms have the same overall structure but differ in key parts, including the catalytic core element P7 and the junctions at which reactions take place. These differences explain the relative stability of the circular species, demonstrate how it is prone to react with a target molecule for circle integration and thus supports the notion that the circular form is a biologically significant molecule possibly with a role in intron mobility.
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Affiliation(s)
- Kasper L Andersen
- Department of Cellular and Molecular Medicine, The Panum Institute, University of Copenhagen, DK-2200 Copenhagen N, Denmark.
| | - Bertrand Beckert
- Department of Cellular and Molecular Medicine, The Panum Institute, University of Copenhagen, DK-2200 Copenhagen N, Denmark.
- Molecular Genetics Genomics Microbiology, Université de Strasbourg, CNRS, UMR 7156, Strasbourg 67081, France.
| | - Benoit Masquida
- Molecular Genetics Genomics Microbiology, Université de Strasbourg, CNRS, UMR 7156, Strasbourg 67081, France.
| | - Steinar D Johansen
- Department of Medical Biology, UiT, The Arctic University of Norway, Tromsø N-9037, Norway.
| | - Henrik Nielsen
- Department of Cellular and Molecular Medicine, The Panum Institute, University of Copenhagen, DK-2200 Copenhagen N, Denmark.
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13
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Petkovic S, Müller S. RNA circularization strategies in vivo and in vitro. Nucleic Acids Res 2015; 43:2454-65. [PMID: 25662225 PMCID: PMC4344496 DOI: 10.1093/nar/gkv045] [Citation(s) in RCA: 233] [Impact Index Per Article: 25.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2014] [Revised: 01/07/2015] [Accepted: 01/12/2015] [Indexed: 12/30/2022] Open
Abstract
In the plenitude of naturally occurring RNAs, circular RNAs (circRNAs) and their biological role were underestimated for years. However, circRNAs are ubiquitous in all domains of life, including eukaryotes, archaea, bacteria and viruses, where they can fulfill diverse biological functions. Some of those functions, as for example playing a role in the life cycle of viral and viroid genomes or in the maturation of tRNA genes, have been elucidated; other putative functions still remain elusive. Due to the resistance to exonucleases, circRNAs are promising tools for in vivo application as aptamers, trans-cleaving ribozymes or siRNAs. How are circRNAs generated in vivo and what approaches do exist to produce ring-shaped RNAs in vitro? In this review we illustrate the occurrence and mechanisms of RNA circularization in vivo, survey methods for the generation of circRNA in vitro and provide appropriate protocols.
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Affiliation(s)
- Sonja Petkovic
- Institut für Biochemie, Ernst Moritz Arndt Universität Greifswald, Felix-Hausdorff-Str. 4, 17487 Greifswald, Germany
| | - Sabine Müller
- Institut für Biochemie, Ernst Moritz Arndt Universität Greifswald, Felix-Hausdorff-Str. 4, 17487 Greifswald, Germany
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14
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RNA folding: structure prediction, folding kinetics and ion electrostatics. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2015; 827:143-83. [PMID: 25387965 DOI: 10.1007/978-94-017-9245-5_11] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Beyond the "traditional" functions such as gene storage, transport and protein synthesis, recent discoveries reveal that RNAs have important "new" biological functions including the RNA silence and gene regulation of riboswitch. Such functions of noncoding RNAs are strongly coupled to the RNA structures and proper structure change, which naturally leads to the RNA folding problem including structure prediction and folding kinetics. Due to the polyanionic nature of RNAs, RNA folding structure, stability and kinetics are strongly coupled to the ion condition of solution. The main focus of this chapter is to review the recent progress in the three major aspects in RNA folding problem: structure prediction, folding kinetics and ion electrostatics. This chapter will introduce both the recent experimental and theoretical progress, while emphasize the theoretical modelling on the three aspects in RNA folding.
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15
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Tang Y, Nielsen H, Masquida B, Gardner PP, Johansen SD. Molecular characterization of a new member of the lariat capping twin-ribozyme introns. Mob DNA 2014; 5:25. [PMID: 25342998 PMCID: PMC4167309 DOI: 10.1186/1759-8753-5-25] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2014] [Accepted: 09/03/2014] [Indexed: 12/20/2022] Open
Abstract
BACKGROUND Twin-ribozyme introns represent a complex class of mobile group I introns that harbour a lariat capping (LC) ribozyme and a homing endonuclease gene embedded in a conventional self-splicing group I ribozyme (GIR2). Twin-ribozyme introns have so far been confined to nucleolar DNA in Naegleria amoeboflagellates and the myxomycete Didymium iridis. RESULTS We characterize structural organization, catalytic properties and molecular evolution of a new twin-ribozyme intron in Allovahlkampfia (Heterolobosea). The intron contains two ribozyme domains with different functions in ribosomal RNA splicing and homing endonuclease mRNA maturation. We found Allovahlkampfia GIR2 to be a typical group IC1 splicing ribozyme responsible for addition of the exogenous guanosine cofactor (exoG), exon ligation and circularization of intron RNA. The Allovahlkampfia LC ribozyme, by contrast, represents an efficient self-cleaving ribozyme that generates a small 2',5' lariat cap at the 5' end of the homing endonuclease mRNA, and thus contributes to intron mobility. CONCLUSIONS The discovery of a twin-ribozyme intron in a member of Heterolobosea expands the distribution pattern of LC ribozymes. We identify a putative regulatory RNA element (AP2.1) in the Allovahlkampfia LC ribozyme that involves homing endonuclease mRNA coding sequences as an important structural component.
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Affiliation(s)
- Yunjia Tang
- RNA and Molecular Pathology group, Department of Medical Biology, Faculty of Health Sciences, UiT - The Arctic University of Norway, MH-building Breivika, N-9037 Tromsø, Norway
- Department of Cellular and Molecular Medicine, The Panum Institute, University of Copenhagen, Copenhagen, Denmark
| | - Henrik Nielsen
- Department of Cellular and Molecular Medicine, The Panum Institute, University of Copenhagen, Copenhagen, Denmark
| | - Benoît Masquida
- Génétique Moléculaire, Génomique, Microbiologie, IPCB, Université de Strasbourg, CNRS, Strasbourg, France
| | - Paul P Gardner
- School of Biological Sciences, University of Canterbury, Christchurch, New Zealand
| | - Steinar D Johansen
- RNA and Molecular Pathology group, Department of Medical Biology, Faculty of Health Sciences, UiT - The Arctic University of Norway, MH-building Breivika, N-9037 Tromsø, Norway
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16
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Hein PP, Kolb KE, Windgassen T, Bellecourt MJ, Darst SA, Mooney RA, Landick R. RNA polymerase pausing and nascent-RNA structure formation are linked through clamp-domain movement. Nat Struct Mol Biol 2014; 21:794-802. [PMID: 25108353 PMCID: PMC4156911 DOI: 10.1038/nsmb.2867] [Citation(s) in RCA: 76] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2014] [Accepted: 07/03/2014] [Indexed: 12/11/2022]
Abstract
The rates of RNA synthesis and the folding of nascent RNA into biologically active structures are linked via pausing by RNA polymerase (RNAP). Structures that form within the RNA-exit channel can either increase pausing by interacting with RNAP or decrease pausing by preventing backtracking. Conversely, pausing is required for proper folding of some RNAs. Opening of the RNAP clamp domain has been proposed to mediate some effects of nascent-RNA structures. However, the connections among RNA structure formation and RNAP clamp movement and catalytic activity remain uncertain. Here, we assayed exit-channel structure formation in Escherichia coli RNAP with disulfide cross-links that favor closed- or open-clamp conformations and found that clamp position directly influences RNA structure formation and RNAP catalytic activity. We report that exit-channel RNA structures slow pause escape by favoring clamp opening through interactions with the flap that slow translocation.
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Affiliation(s)
- Pyae P. Hein
- Department of Biochemistry, University of Wisconsin – Madison, Madison, WI 53706, USA
| | - Kellie E. Kolb
- Department of Biochemistry, University of Wisconsin – Madison, Madison, WI 53706, USA
| | - Tricia Windgassen
- Department of Biochemistry, University of Wisconsin – Madison, Madison, WI 53706, USA
| | - Michael J. Bellecourt
- Department of Biochemistry, University of Wisconsin – Madison, Madison, WI 53706, USA
| | - Seth A. Darst
- Laboratory of Molecular Biophysics, The Rockefeller University, New York, NY 10065, USA
| | - Rachel A. Mooney
- Department of Biochemistry, University of Wisconsin – Madison, Madison, WI 53706, USA
| | - Robert Landick
- Department of Biochemistry, University of Wisconsin – Madison, Madison, WI 53706, USA
- Department of Bacteriology, University of Wisconsin – Madison, Madison, WI 53706, USA
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17
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RNA-RNA interactions and pre-mRNA mislocalization as drivers of group II intron loss from nuclear genomes. Proc Natl Acad Sci U S A 2014; 111:6612-7. [PMID: 24722636 DOI: 10.1073/pnas.1404276111] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Group II introns are commonly believed to be the progenitors of spliceosomal introns, but they are notably absent from nuclear genomes. Barriers to group II intron function in nuclear genomes therefore beg examination. A previous study showed that nuclear expression of a group II intron in yeast results in nonsense-mediated decay and translational repression of mRNA, and that these roadblocks to expression are group II intron-specific. To determine the molecular basis for repression of gene expression, we investigated cellular dynamics of processed group II intron RNAs, from transcription to cellular localization. Our data show pre-mRNA mislocalization to the cytoplasm, where the RNAs are targeted to foci. Furthermore, tenacious mRNA-pre-mRNA interactions, based on intron-exon binding sequences, result in reduced abundance of spliced mRNAs. Nuclear retention of pre-mRNA prevents this interaction and relieves these expression blocks. In addition to providing a mechanistic rationale for group II intron-specific repression, our data support the hypothesis that RNA silencing of the host gene contributed to expulsion of group II introns from nuclear genomes and drove the evolution of spliceosomal introns.
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18
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Lai D, Proctor JR, Meyer IM. On the importance of cotranscriptional RNA structure formation. RNA (NEW YORK, N.Y.) 2013; 19:1461-1473. [PMID: 24131802 PMCID: PMC3851714 DOI: 10.1261/rna.037390.112] [Citation(s) in RCA: 116] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
The expression of genes, both coding and noncoding, can be significantly influenced by RNA structural features of their corresponding transcripts. There is by now mounting experimental and some theoretical evidence that structure formation in vivo starts during transcription and that this cotranscriptional folding determines the functional RNA structural features that are being formed. Several decades of research in bioinformatics have resulted in a wide range of computational methods for predicting RNA secondary structures. Almost all state-of-the-art methods in terms of prediction accuracy, however, completely ignore the process of structure formation and focus exclusively on the final RNA structure. This review hopes to bridge this gap. We summarize the existing evidence for cotranscriptional folding and then review the different, currently used strategies for RNA secondary-structure prediction. Finally, we propose a range of ideas on how state-of-the-art methods could be potentially improved by explicitly capturing the process of cotranscriptional structure formation.
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19
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Zhu JYA, Steif A, Proctor JR, Meyer IM. Transient RNA structure features are evolutionarily conserved and can be computationally predicted. Nucleic Acids Res 2013; 41:6273-85. [PMID: 23625966 PMCID: PMC3695514 DOI: 10.1093/nar/gkt319] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Functional RNA structures tend to be conserved during evolution. This finding is, for example, exploited by comparative methods for RNA secondary structure prediction that currently provide the state-of-art in terms of prediction accuracy. We here provide strong evidence that homologous RNA genes not only fold into similar final RNA structures, but that their folding pathways also share common transient structural features that have been evolutionarily conserved. For this, we compile and investigate a non-redundant data set of 32 sequences with known transient and final RNA secondary structures and devise a dedicated computational analysis pipeline.
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Affiliation(s)
- Jing Yun A Zhu
- Centre for High-Throughput Biology, University of British Columbia, 2125 East Mall, Vancouver, British Columbia V6T 1Z4, Canada
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20
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Proctor JR, Meyer IM. COFOLD: an RNA secondary structure prediction method that takes co-transcriptional folding into account. Nucleic Acids Res 2013; 41:e102. [PMID: 23511969 PMCID: PMC3643587 DOI: 10.1093/nar/gkt174] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Existing state-of-the-art methods that take a single RNA sequence and predict the corresponding RNA secondary structure are thermodynamic methods. These aim to predict the most stable RNA structure. There exists by now ample experimental and theoretical evidence that the process of structure formation matters and that sequences in vivo fold while they are being transcribed. None of the thermodynamic methods, however, consider the process of structure formation. Here, we present a conceptually new method for predicting RNA secondary structure, called CoFold, that takes effects of co-transcriptional folding explicitly into account. Our method significantly improves the state-of-art in terms of prediction accuracy, especially for long sequences of >1000 nt in length.
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Affiliation(s)
- Jeff R Proctor
- Centre for High-Throughput Biology, University of British Columbia, 2125 East Mall, Vancouver, BC, V6T 1Z4, Canada
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21
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Zhao P, Zhang W, Chen SJ. Cotranscriptional folding kinetics of ribonucleic acid secondary structures. J Chem Phys 2012; 135:245101. [PMID: 22225186 DOI: 10.1063/1.3671644] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
We develop a systematic helix-based computational method to predict RNA folding kinetics during transcription. In our method, the transcription is modeled as stepwise process, where each step is the transcription of a nucleotide. For each step, the kinetics algorithm predicts the population kinetics, transition pathways, folding intermediates, and the transcriptional folding products. The folding pathways, rate constants, and the conformational populations for cotranscription folding show contrastingly different features than the refolding kinetics for a fully transcribed chain. The competition between the transcription speed and rate constants for the transitions between the different nascent structures determines the RNA folding pathway and the end product of folding. For example, fast transcription favors the formation of branch-like structures than rod-like structures and chain elongation in the folding process may reduce the probability of the formation of misfolded structures. Furthermore, good theory-experiment agreements suggest that our method may provide a reliable tool for quantitative prediction for cotranscriptional RNA folding, including the kinetics for the population distribution for the whole conformational ensemble.
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Affiliation(s)
- Peinan Zhao
- Department of Physics, Wuhan University, Wuhan, People's Republic of China
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22
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Shui B, Ozer A, Zipfel W, Sahu N, Singh A, Lis JT, Shi H, Kotlikoff MI. RNA aptamers that functionally interact with green fluorescent protein and its derivatives. Nucleic Acids Res 2011; 40:e39. [PMID: 22189104 PMCID: PMC3300005 DOI: 10.1093/nar/gkr1264] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Green Fluorescent Protein (GFP) and related fluorescent proteins (FPs) have been widely used to tag proteins, allowing their expression and subcellular localization to be examined in real time in living cells and animals. Similar fluorescent methods are highly desirable to detect and track RNA and other biological molecules in living cells. For this purpose, we have developed a group of RNA aptamers that bind GFP and related proteins, which we term Fluorescent Protein-Binding Aptamers (FPBA). These aptamers bind GFP, YFP and CFP with low nanomolar affinity and binding decreases GFP fluorescence, whereas slightly augmenting YFP and CFP brightness. Aptamer binding results in an increase in the pKa of EGFP, decreasing the 475 nm excited green fluorescence at a given pH. We report the secondary structure of FPBA and the ability to synthesize functional multivalent dendrimers. FPBA expressed in live cells decreased GFP fluorescence in a valency-dependent manner, indicating that the RNA aptamers function within cells. The development of aptamers that bind fluorescent proteins with high affinity and alter their function, markedly expands their use in the study of biological pathways.
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Affiliation(s)
- Bo Shui
- Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA
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23
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Roychowdhury-Saha M, Roychowdhury S, Burke DH. Conformational heterogeneity and the determinants of tertiary stabilization in the hammerhead ribozyme from Dolichopoda cave crickets. RNA Biol 2011; 8:893-903. [PMID: 21712651 DOI: 10.4161/rna.8.5.16036] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Repetitive DNA elements in Dolichopoda cave cricket genomes contain extended hammerhead ribozymes that are functional in adult crickets, but that exhibit very low self-cleavage activity in vitro relative to other extended hammerhead ribozymes. We find that the parental ribozyme tends to misfold into alternate secondary structures in vitro, complicating analysis of contributions by specific nucleotides to activity under biologically relevant magnesium concentrations. However, minor sequence alterations that stabilize the active secondary structure, without altering candidate tertiary interacting nucleotides, boosted observed rates more than 50-fold (4.4 ± 1.7 min(-1)) and doubled the cleavage extent (>60%) in submillimolar magnesium. Productive alterations included flipping two base pairs in stem I, lengthening stem I and opening stem III to generate a trans-cleaving ribozyme. Specific peripheral nucleotides involved in tertiary stabilization were then identified through kinetic analysis for a series of sequence variants and by correlating plateau cleavage values with band intensity in native gel electrophoresis. These results demonstrate that conformational heterogeneity governs self-cleavage by the wild-type Dolichopoda hammerhead ribozyme in vitro, and they suggest a strategy for improving activity and enhancing the suitability of HHRz for intracellular and biotechnology applications.
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24
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Lemay JF, Desnoyers G, Blouin S, Heppell B, Bastet L, St-Pierre P, Massé E, Lafontaine DA. Comparative study between transcriptionally- and translationally-acting adenine riboswitches reveals key differences in riboswitch regulatory mechanisms. PLoS Genet 2011; 7:e1001278. [PMID: 21283784 PMCID: PMC3024265 DOI: 10.1371/journal.pgen.1001278] [Citation(s) in RCA: 135] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2010] [Accepted: 12/14/2010] [Indexed: 01/08/2023] Open
Abstract
Many bacterial mRNAs are regulated at the transcriptional or translational level by ligand-binding elements called riboswitches. Although they both bind adenine, the adenine riboswitches of Bacillus subtilis and Vibrio vulnificus differ by controlling transcription and translation, respectively. Here, we demonstrate that, beyond the obvious difference in transcriptional and translational modulation, both adenine riboswitches exhibit different ligand binding properties and appear to operate under different regulation regimes (kinetic versus thermodynamic). While the B. subtilis pbuE riboswitch fully depends on co-transcriptional binding of adenine to function, the V. vulnificus add riboswitch can bind to adenine after transcription is completed and still perform translation regulation. Further investigation demonstrates that the rate of transcription is critical for the B. subtilis pbuE riboswitch to perform efficiently, which is in agreement with a co-transcriptional regulation. Our results suggest that the nature of gene regulation control, that is transcription or translation, may have a high importance in riboswitch regulatory mechanisms. Bacterial genetic regulation is mostly performed at the levels of transcription and translation. Recently discovered riboswitches are RNA molecules located in untranslated regions of messenger RNAs that modulate the expression of genes involved in the transport and metabolism of small metabolites. Several riboswitches have recently been shown to employ various regulation mechanisms, but no general rules have yet been deduced from these studies. Here, we have analyzed two adenine-sensing riboswitches of Bacillus subtilis and Vibrio vulnificus that differ by the level at which they control gene expression, which is transcription and translation, respectively. We find that, beyond the obvious difference in transcriptional and translational modulation, riboswitch regulation mechanisms of both adenine riboswitches are fundamentally different. For instance, while the adenine riboswitch from B. subtilis performs co-transcriptional binding for gene regulation, the riboswitch from V. vulnificus relies on reversible ligand binding to achieve gene regulation during mRNA translation. In agreement with co-transcriptional binding of the B. subtilis riboswitch, we find that transcriptional pausing is crucial for gene regulation. Our results suggest that the nature of gene regulation control, that is transcription or translation, may have a high importance in riboswitch regulatory mechanisms.
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Affiliation(s)
- Jean-François Lemay
- Groupe ARN/RNA Group, Département de Biologie, Faculté des Sciences, Université de Sherbrooke, Sherbrooke, Québec, Canada
| | - Guillaume Desnoyers
- Groupe ARN/RNA Group, Département de Biochimie, Faculté de Médecine et Sciences de la Santé, Université de Sherbrooke, Sherbrooke, Québec, Canada
| | - Simon Blouin
- Groupe ARN/RNA Group, Département de Biologie, Faculté des Sciences, Université de Sherbrooke, Sherbrooke, Québec, Canada
| | - Benoit Heppell
- Groupe ARN/RNA Group, Département de Biologie, Faculté des Sciences, Université de Sherbrooke, Sherbrooke, Québec, Canada
| | - Laurène Bastet
- Groupe ARN/RNA Group, Département de Biologie, Faculté des Sciences, Université de Sherbrooke, Sherbrooke, Québec, Canada
| | - Patrick St-Pierre
- Groupe ARN/RNA Group, Département de Biologie, Faculté des Sciences, Université de Sherbrooke, Sherbrooke, Québec, Canada
| | - Eric Massé
- Groupe ARN/RNA Group, Département de Biochimie, Faculté de Médecine et Sciences de la Santé, Université de Sherbrooke, Sherbrooke, Québec, Canada
- * E-mail: (EM); (DL)
| | - Daniel A. Lafontaine
- Groupe ARN/RNA Group, Département de Biologie, Faculté des Sciences, Université de Sherbrooke, Sherbrooke, Québec, Canada
- * E-mail: (EM); (DL)
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25
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Abstract
RNA folding is the most essential process underlying RNA function. While significant progress has been made in understanding the forces driving RNA folding in vitro, exploring the rules governing intracellular RNA structure formation is still in its infancy. The cellular environment hosts a great diversity of factors that potentially influence RNA folding in vivo. For example, the nature of transcription and translation is known to shape the folding landscape of RNA molecules. Trans-acting factors such as proteins, RNAs and metabolites, among others, are also able to modulate the structure and thus the fate of an RNA. Here we summarize the ongoing efforts to uncover how RNA folds in living cells.
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Affiliation(s)
- Georgeta Zemora
- Department of Biochemistry and Cell Biology, Max F. Perutz Laboratories, University of Vienna, Vienna, Austria
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26
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Wang S, Zhao X, Suran R, Vogt VM, Lis JT, Shi H. Knocking down gene function with an RNA aptamer expressed as part of an intron. Nucleic Acids Res 2010; 38:e154. [PMID: 20542918 PMCID: PMC2926621 DOI: 10.1093/nar/gkq529] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
We developed a powerful expression system to produce aptamers and other types of functional RNA in yeast to examine their effects. Utilizing the intron homing process, the aptamer-coding sequences were integrated into hundreds of rRNA genes, and the aptamers were transcribed at high levels by RNA polymerase I without any additional promoter being introduced into the cell. We used this system to express an aptamer against the heat shock factor 1 (HSF1), a conserved transcription factor responsible for mobilizing specific genomic expression programs in response to stressful conditions such as elevated temperature. We observed a temperature sensitive growth retardation phenotype and specific decrease of heat shock gene expression. As HSF1 enables and promotes malignant growth and metastasis in mammals, and this aptamer binds yeast HSF1 and its mammalian ortholog with equal affinity, the results presented here attest to the potential of this aptamer as a specific and effective inhibitor of HSF1 activity.
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Affiliation(s)
- Shengchun Wang
- Department of Biological Sciences and Institute for RNA Science and Technology, University at Albany, State University of New York, Albany, NY 12222 and Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA
| | - Xiaoching Zhao
- Department of Biological Sciences and Institute for RNA Science and Technology, University at Albany, State University of New York, Albany, NY 12222 and Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA
| | - Robert Suran
- Department of Biological Sciences and Institute for RNA Science and Technology, University at Albany, State University of New York, Albany, NY 12222 and Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA
| | - Volker M. Vogt
- Department of Biological Sciences and Institute for RNA Science and Technology, University at Albany, State University of New York, Albany, NY 12222 and Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA
| | - John T. Lis
- Department of Biological Sciences and Institute for RNA Science and Technology, University at Albany, State University of New York, Albany, NY 12222 and Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA
| | - Hua Shi
- Department of Biological Sciences and Institute for RNA Science and Technology, University at Albany, State University of New York, Albany, NY 12222 and Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA
- *To whom correspondence should be addressed. Tel: +1 518 591 8840; Fax: +1 518 442 4767;
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27
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Chalamcharla VR, Curcio MJ, Belfort M. Nuclear expression of a group II intron is consistent with spliceosomal intron ancestry. Genes Dev 2010; 24:827-36. [PMID: 20351053 DOI: 10.1101/gad.1905010] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Group II introns are self-splicing RNAs found in eubacteria, archaea, and eukaryotic organelles. They are mechanistically similar to the metazoan nuclear spliceosomal introns; therefore, group II introns have been invoked as the progenitors of the eukaryotic pre-mRNA introns. However, the ability of group II introns to function outside of the bacteria-derived organelles is debatable, since they are not found in the nuclear genomes of eukaryotes. Here, we show that the Lactococcus lactis Ll.LtrB group II intron splices accurately and efficiently from different pre-mRNAs in a eukaryote, Saccharomyces cerevisiae. However, a pre-mRNA harboring a group II intron is spliced predominantly in the cytoplasm and is subject to nonsense-mediated mRNA decay (NMD), and the mature mRNA from which the group II intron is spliced is poorly translated. In contrast, a pre-mRNA bearing the Tetrahymena group I intron or the yeast spliceosomal ACT1 intron at the same location is not subject to NMD, and the mature mRNA is translated efficiently. Thus, a group II intron can splice from a nuclear transcript, but RNA instability and translation defects would have favored intron loss or evolution into protein-dependent spliceosomal introns, consistent with the bacterial group II intron ancestry hypothesis.
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28
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Abstract
RNA folds during transcription in the cell. Compared to most in vitro studies where the focus is generally on Mg(2+)-initiated refolding of fully synthesized transcripts, cotranscriptional RNA folding studies better replicate how RNA folds in a cellular environment. Unique aspects of cotranscriptional folding include the 5'- to 3'-polarity of RNA, the transcriptional speed, pausing properties of the RNA polymerase, the effect of the transcriptional complex and associated factors, and the effect of RNA-binding proteins. Identifying strategic pause sites can reveal insights on the folding pathway of the nascent transcript. Structural mapping of the paused transcription complexes identifies important folding intermediates along these pathways. Oligohybridization assays and the appearance of the catalytic activity of a ribozyme either in trans or in cis can be used to monitor cotranscriptional folding under a wide range of conditions. In our laboratory, these methodologies have been applied to study the folding of three highly conserved RNAs (RNase P, SRP, and tmRNA), several circularly permuted forms of a bacterial RNase P RNA, a riboswitch (thiM), and an aptamer-activated ribozyme (glmS).
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Affiliation(s)
- Terrence N Wong
- Department of Biochemistry & Molecular Biology, University of Chicago, Chicago, Illinois, USA
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29
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Dotson PP, Johnson AK, Testa SM. Tetrahymena thermophila and Candida albicans group I intron-derived ribozymes can catalyze the trans-excision-splicing reaction. Nucleic Acids Res 2008; 36:5281-9. [PMID: 18684993 PMCID: PMC2532722 DOI: 10.1093/nar/gkn507] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Group I intron-derived ribozymes can catalyze a variety of non-native reactions. For the trans-excision-splicing (TES) reaction, an intron-derived ribozyme from the opportunistic pathogen Pneumocystis carinii catalyzes the excision of a predefined region from within an RNA substrate with subsequent ligation of the flanking regions. To establish TES as a general ribozyme-mediated reaction, intron-derived ribozymes from Tetrahymena thermophila and Candida albicans, which are similar to but not the same as that from Pneumocystis, were investigated for their propensity to catalyze the TES reaction. We now report that the Tetrahymena and Candida ribozymes can catalyze the excision of a single nucleotide from within their ribozyme-specific substrates. Under the conditions studied, the Tetrahymena and Candida ribozymes, however, catalyze the TES reaction with lower yields and rates [Tetrahymena (k(obs)) = 0.14/min and Candida (k(obs)) = 0.34/min] than the Pneumocystis ribozyme (k(obs) = 3.2/min). The lower yields are likely partially due to the fact that the Tetrahymena and Candida catalyze additional reactions, separate from TES. The differences in rates are likely partially due to the individual ribozymes ability to effectively bind their 3' terminal guanosines as intramolecular nucleophiles. Nevertheless, our results demonstrate that group I intron-derived ribozymes are inherently able to catalyze the TES reaction.
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Affiliation(s)
- P Patrick Dotson
- Department of Chemistry, University of Kentucky, Lexington, KY 40506, USA
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30
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Toxic introns and parasitic intein in Coxiella burnetii: legacies of a promiscuous past. J Bacteriol 2008; 190:5934-43. [PMID: 18606739 DOI: 10.1128/jb.00602-08] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
The genome of the obligate intracellular pathogen Coxiella burnetii contains a large number of selfish genetic elements, including two group I introns (Cbu.L1917 and Cbu.L1951) and an intervening sequence that interrupts the 23S rRNA gene, an intein (Cbu.DnaB) within dnaB and 29 insertion sequences. Here, we describe the ability of the intron-encoded RNAs (ribozymes) to retard bacterial growth rate (toxicity) and examine the functionality and phylogenetic history of Cbu.DnaB. When expressed in Escherichia coli, both introns repressed growth, with Cbu.L1917 being more inhibitory. Both ribozymes were found to associate with ribosomes of Coxiella and E. coli. In addition, ribozymes significantly reduced in vitro luciferase translation, again with Cbu.L1917 being more inhibitory. We analyzed the relative quantities of ribozymes and genomes throughout a 14-day growth cycle of C. burnetii and found that they were inversely correlated, suggesting that the ribozymes have a negative effect on Coxiella's growth. We determined possible sites for ribozyme associations with 23S rRNA that could explain the observed toxicities. Further research is needed to determine whether the introns are being positively selected because they promote bacterial persistence or whether they were fixed in the population due to genetic drift. The intein, Cbu.DnaB, is able to self-splice, leaving the host protein intact and presumably functional. Similar inteins have been found in two extremophilic bacteria (Alkalilimnicola ehrlichei and Halorhodospira halophila) that are distantly related to Coxiella, making it difficult to determine whether the intein was acquired by horizontal gene transfer or was vertically inherited from a common ancestor.
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31
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Dotson PP, Sinha J, Testa SM. A Pneumocystis carinii group I intron-derived ribozyme utilizes an endogenous guanosine as the first reaction step nucleophile in the trans excision-splicing reaction. Biochemistry 2008; 47:4780-7. [PMID: 18363339 DOI: 10.1021/bi7020525] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In the trans excision-splicing reaction, a Pneumocystis carinii group I intron-derived ribozyme binds an RNA substrate, excises a specific internal segment, and ligates the flanking regions back together. This reaction can occur both in vitro and in vivo. In this report, the first of the two reaction steps was analyzed to distinguish between two reaction mechanisms: ribozyme-mediated hydrolysis and nucleotide-dependent intramolecular transesterification. We found that the 3'-terminal nucleotide of the ribozyme is the first-reaction step nucleophile. In addition, the 3'-half of the RNA substrate becomes covalently attached to the 3'-terminal nucleotide of the ribozyme during the reaction, both in vitro and in vivo. Results also show that the identity of the 3'-terminal nucleotide influences the rate of the intramolecular transesterification reaction, with guanosine being more effective than adenosine. Finally, expected products of the hydrolysis mechanism do not form during the reaction. These results are consistent with only the intramolecular transesterification mechanism. Unexpectedly, we also found that ribozyme constructs become truncated in vivo, probably through intramolecular 3'-hydrolysis (self-activation), to create functional 3'-terminal nucleotides.
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Affiliation(s)
- P Patrick Dotson
- Department of Chemistry, University of Kentucky, Lexington, KY 40506, USA
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Jackson SA, Koduvayur S, Woodson SA. Self-splicing of a group I intron reveals partitioning of native and misfolded RNA populations in yeast. RNA (NEW YORK, N.Y.) 2006; 12:2149-59. [PMID: 17135489 PMCID: PMC1664722 DOI: 10.1261/rna.184206] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Stable RNAs must form specific three-dimensional structures, yet many RNAs become kinetically trapped in misfolded conformations. To understand the factors that control the accuracy of RNA folding in the cell, the self-splicing activity of the Tetrahymena group I intron was compared in different genetic contexts in budding yeast. The extent of splicing was 98% when the intron was placed in its natural rDNA context, but only 3% when the intron was expressed in an exogenous pre-mRNA. Further experiments showed that the probability of forming the active intron structure depends on local sequence context and transcription by Pol I. Pre-rRNAs decayed at similar rates, whether the intron was wild type or inactivated by an internal deletion, suggesting that most of the unreacted pre-rRNA is incompetent to splice. Northern blots and complementation assays showed that mutations that destabilize the intron tertiary structure inhibited self-splicing and processing of internal transcribed spacer 2. The data are consistent with partitioning of pre-rRNAs into active and inactive populations. The misfolded RNAs are sequestered and degraded without refolding to a significant extent. Thus, the initial fidelity of folding can dictate the intracellular fate of transcripts containing this group I intron.
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Affiliation(s)
- Scott A Jackson
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, USA
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33
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Abstract
The evolution of RNA sequence needs to satisfy three requirements: folding, structure, and function. Studies on folding during transcription are related directly to folding in the cell. Understanding RNA folding during transcription requires the elucidation of structure formation and structural changes of the RNA, and the consideration of intrinsic properties of the RNA polymerase and other proteins that interact with the RNA. This review summarizes the research progress in this area and outlines the enormous challenges facing this field. Significant advancement requires the development of new experimental methods and theoretical considerations in all aspects of transcription and RNA folding.
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Affiliation(s)
- Tao Pan
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois 60637, USA.
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Koduvayur SP, Woodson SA. Intracellular folding of the Tetrahymena group I intron depends on exon sequence and promoter choice. RNA (NEW YORK, N.Y.) 2004; 10:1526-32. [PMID: 15337845 PMCID: PMC1370639 DOI: 10.1261/rna.7880404] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
The Tetrahymena group I intron splices 20 to 50 times faster in Tetrahymena than in vitro, implying that the intron rapidly adopts its active conformation in the cell. The importance of cotranscriptional folding and the contribution of the rRNA exons to the stability of the active pre-RNA structure were investigated by comparing the activity of minimal pre-RNAs expressed in Escherichia coli. Pre-RNAs containing exons derived from E. coli 23 S rRNA were three to four times more active than the wild-type Tetrahymena pre-RNA. E. coli transcripts of the chimeric E. coli pre-RNA were two to eight times more active than were T7 transcripts. However, the effect of cotranscriptional folding depends on exon sequences. Unexpectedly, the unspliced pre-RNA decays more slowly than predicted from the rate of splicing. This observation is best explained by partitioning of transcripts into active and inactive pools. We propose that the active pool splices within a few seconds, whereas the inactive pool is degraded without appreciable splicing.
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Affiliation(s)
- Sujatha P Koduvayur
- Department of Biophysics, Johns Hopkins University, 3400 N. Charles St., Baltimore, Maryland 21218, USA
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35
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Jacob NK, Stout AR, Price CM. Modulation of telomere length dynamics by the subtelomeric region of tetrahymena telomeres. Mol Biol Cell 2004; 15:3719-28. [PMID: 15169872 PMCID: PMC491831 DOI: 10.1091/mbc.e04-03-0237] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Tetrahymena telomeres usually consist of approximately 250 base pairs of T(2)G(4) repeats, but they can grow to reach a new length set point of up to 900 base pairs when kept in log culture at 30 degrees C. We have examined the growth profile of individual macronuclear telomeres and have found that the rate and extent of telomere growth are affected by the subtelomeric region. When the sequence of the rDNA subtelomeric region was altered, we observed a decrease in telomere growth regardless of whether the GC content was increased or decreased. In both cases, the ordered structure of the subtelomeric chromatin was disrupted, but the effect on the telomeric complex was relatively minor. Examination of the telomeres from non-rDNA chromosomes showed that each telomere exhibited a unique and characteristic growth profile. The subtelomeric regions from individual chromosome ends did not share common sequence elements, and they each had a different chromatin structure. Thus, telomere growth is likely to be regulated by the organization of the subtelomeric chromatin rather than by a specific DNA element. Our findings suggest that at each telomere the telomeric complex and subtelomeric chromatin cooperate to form a unique higher order chromatin structure that controls telomere length.
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Affiliation(s)
- Naduparambil K Jacob
- Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0524, USA
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36
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Lundblad EW, Einvik C, Rønning S, Haugli K, Johansen S. Twelve Group I introns in the same pre-rRNA transcript of the myxomycete Fuligo septica: RNA processing and evolution. Mol Biol Evol 2004; 21:1283-93. [PMID: 15034133 DOI: 10.1093/molbev/msh126] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The ribosomal DNA region of the myxomycete Fuligo septica was investigated and found to contain 12 group I introns (four in the small subunit and eight in the large subunit ribosomal RNAs). We have performed molecular and phylogenetic analyses to provide insight into intron structure and function, intron-host biology, and intron origin and evolution. The introns vary in size from 398 to 943 nt, all lacking detectable open reading frames. Secondary structure models revealed considerable structural diversity, but all, except one (subclass IB), represent the common group IC1 intron subclass. In vitro splicing analysis revealed that 10 of the 12 introns were able to self-splice as naked RNA, but all 12 introns were able to splice out from the precursor rRNA in vivo as evaluated by reverse transcription PCR analysis on total F. septica RNA. Furthermore, RNA processing analyses in vitro and in vivo showed that 10 of 12 introns perform hydrolytic cleavage at the 3' splice site, as well as intron circularization. Full-length intron RNA circles were detected in vivo. The order of splicing was analyzed by a reverse transcription PCR approach on cellular RNA, but no strict order of intron excision could be detected. Phylogenetic analysis indicated that most Fuligo introns were distantly related to each other and were independently gained in ribosomal DNA during evolution.
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Affiliation(s)
- Eirik W Lundblad
- Department of Molecular Biotechnology, RNA research group, Institute of Medical Biology, University of Tromso, Tromso, Norway
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Nielsen H, Fiskaa T, Birgisdottir AB, Haugen P, Einvik C, Johansen S. The ability to form full-length intron RNA circles is a general property of nuclear group I introns. RNA (NEW YORK, N.Y.) 2003; 9:1464-1475. [PMID: 14624003 PMCID: PMC1370501 DOI: 10.1261/rna.5290903] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2003] [Accepted: 08/28/2003] [Indexed: 05/24/2023]
Abstract
In addition to splicing, group I intron RNA is capable of an alternative two-step processing pathway that results in the formation of full-length intron circular RNA. The circularization pathway is initiated by hydrolytic cleavage at the 3' splice site and followed by a transesterification reaction in which the intron terminal guanosine attacks the 5' splice site presented in a structure analogous to that of the first step of splicing. The products of the reactions are full-length circular intron and unligated exons. For this reason, the circularization reaction is to the benefit of the intron at the expense of the host. The circularization pathway has distinct structural requirements that differ from those of splicing and appears to be specifically suppressed in vivo. The ability to form full-length circles is found in all types of nuclear group I introns, including those from the Tetrahymena ribosomal DNA. The biological function of the full-length circles is not known, but the fact that the circles contain the entire genetic information of the intron suggests a role in intron mobility.
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Affiliation(s)
- Henrik Nielsen
- Department of Medical Biochemistry and Genetics, The Panum Institute, University of Copenhagen, DK-2200 Copenhagen, Denmark
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38
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Heilman-Miller SL, Woodson SA. Effect of transcription on folding of the Tetrahymena ribozyme. RNA (NEW YORK, N.Y.) 2003; 9:722-33. [PMID: 12756330 PMCID: PMC1370439 DOI: 10.1261/rna.5200903] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2003] [Accepted: 03/11/2003] [Indexed: 05/20/2023]
Abstract
Sequential formation of RNA interactions during transcription can bias the folding pathway and ultimately determine the functional state of a transcript. The kinetics of cotranscriptional folding of the Tetrahymena L-21 ribozyme was compared with refolding of full-length transcripts under the same conditions. Sequential folding after transcription by phage T7 or Escherichia coli polymerase is only twice as fast as refolding, and the yield of native RNA is the same. By contrast, a greater fraction of circularly permuted variants folded correctly at early times during transcription than during refolding. Hybridization of complementary oligonucleotides suggests that cotranscriptional folding enables a permuted RNA beginning at G303 to escape non-native interactions in P3 and P9. We propose that base pairing of upstream sequences during transcription elongation favors branched secondary structures that increase the probability of forming the native ribozyme structure.
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Affiliation(s)
- Susan L Heilman-Miller
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742-2021, USA
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39
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Affiliation(s)
- R Kierzek
- Institute of Bioorganic Chemistry, Polish Academy of Sciences, 61-704 Poznañ, Poland
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40
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Abstract
To learn more about the structure of the DNA terminus at Tetrahymena thermophila telomeres, we have devised a ligation-mediated primer extension protocol to accurately measure the length of the G-strand overhang. We show that overhang length and the identity of the 3'-terminal nucleotide are tightly regulated. The majority of overhangs terminate in the sequence 5'-TTGGGGT and >80% are either 14-15 or 20-21 nucleotides in length. No significant changes in overhang length were detected as cells traversed the cell cycle. However, changes in length distribution were observed when cells exited the cell cycle, indicating an altered balance between DNA synthesis and degradation or end protection. We also provide evidence that rDNA molecules have overhangs on both telomeres. Full-length rDNA could be cloned by a strategy that depends on overhangs being present at both ends. Moreover, analysis of leading strand telomeres revealed that a significant fraction have overhangs > or =5 nucleotides. Our results indicate that generation of the terminal telomeric DNA structure is highly regulated and requires several distinct DNA-processing events.
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Affiliation(s)
| | - Rose Skopp
- Department of Molecular Genetics, Biochemistry and Microbiology, School of Medicine, University of Cincinnati, ML0524, 231 Albert Sabin Way, Cincinnati, OH 45267 and
Department of Veterinary Science, University of Nebraska, Lincoln, NE 68588, USA Corresponding author e-mail:
| | - Carolyn M. Price
- Department of Molecular Genetics, Biochemistry and Microbiology, School of Medicine, University of Cincinnati, ML0524, 231 Albert Sabin Way, Cincinnati, OH 45267 and
Department of Veterinary Science, University of Nebraska, Lincoln, NE 68588, USA Corresponding author e-mail:
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41
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Abstract
In some ciliates, the DNA sequences of the germline genomes have been profoundly modified during evolution, providing unprecedented examples of germline DNA malleability. Although the significance of the modifications and malleability is unclear, they may reflect the evolution of mechanisms that facilitate evolution. Because of the modifications, these ciliates must perform remarkable feats of cutting, splicing, rearrangement and elimination of DNA sequences to convert the chromosomal DNA in the germline genome (micronuclear genome) into gene-sized DNA molecules in the somatic genome (macronuclear genome). How these manipulations of DNA are guided and carried out is largely unknown. However, the organization and manipulation of ciliate DNA sequences are new phenomena that expand a general appreciation for the flexibility of DNA in evolution and development.
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Affiliation(s)
- D M Prescott
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309-0347, USA.
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42
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Abstract
Treatment of genetic disorders by gene therapy has conventionally been attempted through the transfer of a wild type version of a gene to the cells of a patient harboring defective copies of a disease associated gene. Despite significant advances using this paradigm, several technical hurdles must still be overcome before this 'gene replacement' approach will become useful in the treatment of a variety of genetic maladies. Such limitations have led a number of researchers to begin to investigate alternative strategies to genetic therapy. Repair of mutant genetic instructions represents a fundamentally different approach to genetic therapy that may have significant advantages over gene replacement. Herein, we will discuss recent advances using repair of mutant RNAs as a novel means to correct genetic deficiencies.
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Affiliation(s)
- T Watanabe
- Center for Genetic and Cellular Therapies, Departments of Surgery and Genetics, Duke University Medical Center, Durham, NC 27710, USA
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43
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Abstract
The hairpin ribozyme belongs to the family of small catalytic RNAs that cleave RNA substrates in a reversible reaction that generates 2',3'-cyclic phosphate and 5'-hydroxyl termini. The hairpin catalytic motif was discovered in the negative strand of the tobacco ringspot virus satellite RNA, where hairpin ribozyme-mediated self-cleavage and ligation reactions participate in processing RNA replication intermediates. The self-cleaving hairpin, hammerhead, hepatitis delta and Neurospora VS RNAs each adopt unique structures and exploit distinct kinetic and catalytic mechanisms despite catalyzing the same chemical reactions. Mechanistic studies of hairpin ribozyme reactions provided early evidence that, like protein enzymes, RNA enzymes are able to exploit a variety of catalytic strategies. In contrast to the hammerhead and Tetrahymena ribozyme reactions, hairpin-mediated cleavage and ligation proceed through a catalytic mechanism that does not require direct coordination of metal cations to phosphate or water oxygens. The hairpin ribozyme is a better ligase than it is a nuclease while the hammerhead reaction favors cleavage over ligation of bound products by nearly 200-fold. Recent structure-function studies have begun to yield insights into the molecular bases of these unique features of the hairpin ribozyme.
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Affiliation(s)
- M J Fedor
- Department of Molecular Biology and the Skaggs Institute for Chemical Biology, The Scripps Research Institute, MB35, 10550 N. Torrey Pines Road, La Jolla, CA 92037, USA.
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Donahue CP, Yadava RS, Nesbitt SM, Fedor MJ. The kinetic mechanism of the hairpin ribozyme in vivo: influence of RNA helix stability on intracellular cleavage kinetics. J Mol Biol 2000; 295:693-707. [PMID: 10623557 DOI: 10.1006/jmbi.1999.3380] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The relationship between hairpin ribozyme structure, and cleavage and ligation kinetics, and equilibria has been characterized extensively under a variety of reaction conditions in vitro. We developed a quantitative assay of hairpin ribozyme cleavage activity in yeast to learn how structure-function relationships defined for RNA enzymes in vitro relate to RNA-mediated reactions in cells. Here, we report the effects of variation in the stability of an essential secondary structure element, H1, on intracellular cleavage kinetics. H1 is the base-paired helix formed between ribozyme and 3' cleavage product RNAs. H1 sequences with fewer than three base-pairs fail to support full activity in vitro or in vivo, arguing against any significant difference in the stability of short RNA helices under in vitro and intracellular conditions. Under standard conditions in vitro that include 10 mM MgCl(2), the internal equilibrium between cleavage and ligation of ribozyme-bound products favors ligation. Consequently, ribozymes with stable H1 sequences display sharply reduced self-cleavage rates, because cleavage is reversed by rapid re-ligation of bound products. In contrast, ribozymes with as many as 26 base-pairs in H1 continue to self-cleave at maximum rates in vivo. The failure of large products to inhibit cleavage could be explained if intracellular conditions promote rapid product dissociation or shift the internal equilibrium to favor cleavage. Model experiments in vitro suggest that the internal equilibrium between cleavage and ligation of bound products is likely to favor cleavage under intracellular ionic conditions.
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Affiliation(s)
- C P Donahue
- Department of Molecular Biology, Skaggs Institute for Chemical Biology, The Scripps Research Institute, MB35, 10550 N. Torrey Pines Rd, La Jolla, CA, 92037, USA
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45
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Ho Y, Waring RB. The maturase encoded by a group I intron from Aspergillus nidulans stabilizes RNA tertiary structure and promotes rapid splicing. J Mol Biol 1999; 292:987-1001. [PMID: 10512698 DOI: 10.1006/jmbi.1999.3070] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The AnCOB group I intron from Aspergillus nidulans self-splices, providing the Mg2+ concentration is >/= 15 mM. The splicing reaction is greatly stimulated by a maturase protein encoded within the intron itself. An initial structural and biochemical analysis of the splicing reaction has now been performed. The maturase bound rapidly to the precursor RNA (kon approximately 3 x 10(9) M(-1) min(-1)) and remained tightly bound (koff </= 0.04 min(-1)). The catalytic step of 5' splice-site cleavage occurred at a rate of up to 11 min(-1) under single turnover conditions. The maturase-assisted reaction of heat-denatured RNA proceeded at a rate of about 1 min(-1), arguing that there are early steps of folding that cannot be readily facilitated by the protein. pH analysis revealed a biphasic profile with a pKa of 7.0. The rate of the maturase-assisted reaction was independent of the Mg2+ concentration down to 3 mM. Self-splicing in optimal Mg2+ (>/= 150 mM) was tenfold slower, in part because of the existence of an equilibrium between folded and partially folded RNA. In contrast, the maturase very effectively stabilized tertiary structure in 5 mM Mg2+, a noticeable example being an interaction between the P8 helix and a GNRA sequence that constitutes the L2 terminal loop of the P2 helix. Formation of the 5' splice-site recognition helix was assisted by either the maturase or high concentrations of Mg2+. The maturase was required during splicing so it is not a true chaperone. However, RNase protection assays and kinetic studies suggest that the maturase recognizes and facilitates folding of an intron with limited tertiary structure and even incomplete secondary structure.
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Affiliation(s)
- Y Ho
- Department of Biology, Temple University, Philadelphia, PA 19122, USA
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46
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Abstract
Recent reports have demonstrated that the group I ribozyme from Tetrahymena thermophila can perform trans-splicing reactions to repair mutant RNAs. For therapeutic use, such ribozymes must function efficiently when transcribed from genes delivered to human cells, yet it is unclear how group I splicing reactions are influenced by intracellular expression of the ribozyme. Here we evaluate the self-splicing efficiency of group I introns from transcripts expressed by RNA polymerase II in human cells to directly measure ribozyme catalysis in a therapeutically relevant setting. Intron-containing expression cassettes were transfected into a human cell line, and RNA transcripts were analyzed for intron removal. The percentage of transcripts that underwent self-splicing ranged from 0 to 50%, depending on the construct being tested. Thus, self-splicing activity is supported in the mammalian cellular environment. However, we find that the extent of self-splicing is greatly influenced by sequences flanking the intron and presumably reflects differences in the intron's ability to fold into an active conformation inside the cell. In support of this hypothesis, we show that the ability of the intron to fold and self-splice from cellular transcripts in vitro correlates well with the catalytic efficiency observed from the same transcripts expressed inside cells. These results underscore the importance of evaluating the impact of sequence context on the activity of therapeutic group I ribozymes. The self-splicing system that we describe should facilitate these efforts as well as aid in efforts at enhancing in vivo ribozyme activity for various applications of RNA repair.
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Affiliation(s)
- M B Long
- Departments of Genetics and Surgery, Center for Genetic and Cellular Therapies, Duke University Medical Center, Durham, North Carolina 27710, USA
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47
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Nikolcheva T, Woodson SA. Facilitation of group I splicing in vivo: misfolding of the Tetrahymena IVS and the role of ribosomal RNA exons. J Mol Biol 1999; 292:557-67. [PMID: 10497021 DOI: 10.1006/jmbi.1999.3083] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Self-splicing of the group I IVS from Tetrahymena thermophila rDNA is limited by the time required for the RNA to reach its active conformation. In vitro, folding is slow because the pre-rRNA becomes kinetically trapped in inactive structures. In vivo, splicing is 50 times more rapid, implying that misfolding of the pre-rRNA is corrected. Exon mutations that inhibit self-splicing 100-fold in vitro were fully rescued when the pre-rRNA containing the IVS was expressed in E. coli. In contrast, IVS mutations that cause misfolding were only partially suppressed at 42 degrees C, and doubled the activation energy of splicing. These results suggest that intracellular folding of the pre-rRNA involves metastable intermediates similar to those observed in vitro. Precursors with natural rRNA exons were more active and less cold-sensitive than those with non-rRNA exons. This shows that the rRNA reduces misfolding of the IVS, thereby facilitating splicing of the pre-rRNA in vivo.
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Affiliation(s)
- T Nikolcheva
- Program in Molecular and Cell Biology, University of Maryland, College Park, MD 20742-2021, USA
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48
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Pan T, Artsimovitch I, Fang XW, Landick R, Sosnick TR. Folding of a large ribozyme during transcription and the effect of the elongation factor NusA. Proc Natl Acad Sci U S A 1999; 96:9545-50. [PMID: 10449729 PMCID: PMC22245 DOI: 10.1073/pnas.96.17.9545] [Citation(s) in RCA: 114] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We compared in vitro transcription-initiated folding of the ribozyme from Bacillus subtilis RNase P to refolding from the full-length, denatured state by monitoring the appearance of its catalytic activity. At 37 degrees C, Mg(2+)-initiated refolding of the wild type and a circularly permutate ribozyme takes minutes and is limited by a kinetic trap. Transcription by T7 RNA polymerase alters the folding pathway of both RNAs and introduces new kinetic traps. Transcription by the core Escherichia coli RNA polymerase yields the same result, in spite of its 4-fold-slower elongation rate. However, the presence of its elongation factor NusA accelerates more than 10-fold the transcription-initiated folding of the circularly, permutated ribozyme by E. coli RNA polymerase. The effect of NusA likely is caused by its enhancement of transcriptional pausing because NusA did not accelerate transcription-initiated folding using a mutant RNA polymerase that failed to pause or respond to NusA during ribozyme synthesis. We conclude that both transcription and specific pausing therein can alter RNA-folding pathways.
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Affiliation(s)
- T Pan
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL 60637, USA.
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49
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Vader A, Nielsen H, Johansen S. In vivo expression of the nucleolar group I intron-encoded I-dirI homing endonuclease involves the removal of a spliceosomal intron. EMBO J 1999; 18:1003-13. [PMID: 10022842 PMCID: PMC1171192 DOI: 10.1093/emboj/18.4.1003] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The Didymium iridis DiSSU1 intron is located in the nuclear SSU rDNA and has an unusual twin-ribozyme organization. One of the ribozymes (DiGIR2) catalyses intron excision and exon ligation. The other ribozyme (DiGIR1), which along with the endonuclease-encoding I-DirI open reading frame (ORF) is inserted in DiGIR2, carries out hydrolysis at internal processing sites (IPS1 and IPS2) located at its 3' end. Examination of the in vivo expression of DiSSU1 shows that after excision, DiSSU1 is matured further into the I-DirI mRNA by internal DiGIR1-catalysed cleavage upstream of the ORF 5' end, as well as truncation and polyadenylation downstream of the ORF 3' end. A spliceosomal intron, the first to be reported within a group I intron and the rDNA, is removed before the I-DirI mRNA associates with the polysomes. Taken together, our results imply that DiSSU1 uses a unique combination of intron-supplied ribozyme activity and adaptation to the general RNA polymerase II pathway of mRNA expression to allow a protein to be produced from the RNA polymerase I-transcribed rDNA.
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Affiliation(s)
- A Vader
- Department of Molecular Cell Biology, Institute of Medical Biology, University of Tromso, N-9037 Tromso, Norway.
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50
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Group I introns in biotechnology: prospects of application of ribozymes and rare-cutting homing endonucleases. ACTA ACUST UNITED AC 1997. [DOI: 10.1016/s1387-2656(08)70031-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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