1
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Shen A, Hencel K, Parker MT, Scott R, Skukan R, Adesina AS, Metheringham CL, Miska EA, Nam Y, Haerty W, Simpson GG, Akay A. U6 snRNA m6A modification is required for accurate and efficient splicing of C. elegans and human pre-mRNAs. Nucleic Acids Res 2024:gkae447. [PMID: 38808663 DOI: 10.1093/nar/gkae447] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2023] [Revised: 05/08/2024] [Accepted: 05/13/2024] [Indexed: 05/30/2024] Open
Abstract
pre-mRNA splicing is a critical feature of eukaryotic gene expression. Both cis- and trans-splicing rely on accurately recognising splice site sequences by spliceosomal U snRNAs and associated proteins. Spliceosomal snRNAs carry multiple RNA modifications with the potential to affect different stages of pre-mRNA splicing. Here, we show that the conserved U6 snRNA m6A methyltransferase METT-10 is required for accurate and efficient cis- and trans-splicing of C. elegans pre-mRNAs. The absence of METT-10 in C. elegans and METTL16 in humans primarily leads to alternative splicing at 5' splice sites with an adenosine at +4 position. In addition, METT-10 is required for splicing of weak 3' cis- and trans-splice sites. We identified a significant overlap between METT-10 and the conserved splicing factor SNRNP27K in regulating 5' splice sites with +4A. Finally, we show that editing endogenous 5' splice site +4A positions to +4U restores splicing to wild-type positions in a mett-10 mutant background, supporting a direct role for U6 snRNA m6A modification in 5' splice site recognition. We conclude that the U6 snRNA m6A modification is important for accurate and efficient pre-mRNA splicing.
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Affiliation(s)
- Aykut Shen
- School of Biological Sciences, University of East Anglia, NR4 7TJ Norwich, UK
| | - Katarzyna Hencel
- School of Biological Sciences, University of East Anglia, NR4 7TJ Norwich, UK
| | - Matthew T Parker
- School of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - Robyn Scott
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Roberta Skukan
- School of Biological Sciences, University of East Anglia, NR4 7TJ Norwich, UK
| | | | | | - Eric A Miska
- Wellcome/CRUK Gurdon Institute, University of Cambridge, Tennis Court Rd, Cambridge CB2 1QN, UK
| | - Yunsun Nam
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX, USA
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA
- Simmons Comprehensive Cancer Center, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Wilfried Haerty
- School of Biological Sciences, University of East Anglia, NR4 7TJ Norwich, UK
- Earlham Institute, Norwich Research Park, Norwich, UK
| | - Gordon G Simpson
- School of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK
- Cell & Molecular Sciences, James Hutton Institute, Invergowrie, DD2 5DA, UK
| | - Alper Akay
- School of Biological Sciences, University of East Anglia, NR4 7TJ Norwich, UK
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2
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Haack DB, Rudolfs B, Zhang C, Lyumkis D, Toor N. Structural basis of branching during RNA splicing. Nat Struct Mol Biol 2024; 31:179-189. [PMID: 38057551 PMCID: PMC10968580 DOI: 10.1038/s41594-023-01150-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2023] [Accepted: 10/04/2023] [Indexed: 12/08/2023]
Abstract
Branching is a critical step in RNA splicing that is essential for 5' splice site selection. Recent spliceosome structures have led to competing models for the recognition of the invariant adenosine at the branch point. However, there are no structures of any splicing complex with the adenosine nucleophile docked in the active site and positioned to attack the 5' splice site. Thus we lack a mechanistic understanding of adenosine selection and splice site recognition during RNA splicing. Here we present a cryo-electron microscopy structure of a group II intron that reveals that active site dynamics are coupled to the formation of a base triple within the branch-site helix that positions the 2'-OH of the adenosine for nucleophilic attack on the 5' scissile phosphate. This structure, complemented with biochemistry and comparative analyses to splicing complexes, supports a base triple model of adenosine recognition for branching within group II introns and the evolutionarily related spliceosome.
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Affiliation(s)
- Daniel B Haack
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA, USA.
| | - Boris Rudolfs
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA, USA
| | - Cheng Zhang
- Salk Institute, La Jolla, CA, USA
- Amgen, Thousand Oaks, CA, USA
| | | | - Navtej Toor
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA, USA.
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3
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Seabolt MH, Roellig DM, Konstantinidis KT. Spliceosomal introns in the diplomonad parasite Giardia duodenalis revisited. Microb Genom 2023; 9. [PMID: 37934076 DOI: 10.1099/mgen.0.001117] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2023] Open
Abstract
Complete reference genomes, including correct feature annotations, are a fundamental aspect of genomic biology. In the case of protozoan species such as Giardia duodenalis, a major human and animal parasite worldwide, accurate genome annotation can deepen our understanding of the evolution of parasitism and pathogenicity by identifying genes underlying key traits and clinically relevant cellular mechanisms, and by extension, the development of improved prevention strategies and treatments. This study used bioinformatics analyses of Giardia mRNA libraries to characterize known introns and identify new intron candidates, working towards completion of the G. duodenalis assemblage A strain 'WB' genome and further elucidating Giardia's gene expression. By using a set of experimentally validated positive control loci to calibrate our intron detection pipeline, we were able to detect evidence of previously missed candidate splice junctions directly from expressed transcript data. These intron candidates were further studied in silico using NMDS (non-metric multidimensional scaling) clustering to determine shared characteristics and their relative importance such as secondary structure, splicing efficiency and motif conservation, and thus to refine intron models. Results from this study identified 34 new intron candidates, with several potential introns showing evidence that secondary structure of the mRNA molecule might play a more significant role in splicing than previously reported eukaryotic splicing activity mediated by a reduced spliceosome present in G. duodenalis.
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Affiliation(s)
- Matthew H Seabolt
- Division of Foodborne, Waterborne, and Environmental Diseases, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, GA 30329, USA
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA 30332, USA
- Leidos Inc., Reston, VA 20190, USA
| | - Dawn M Roellig
- Division of Foodborne, Waterborne, and Environmental Diseases, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, GA 30329, USA
| | - Konstantinos T Konstantinidis
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA 30332, USA
- School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA
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4
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Shen A, Hencel K, Parker MT, Scott R, Skukan R, Adesina AS, Metheringham CL, Miska EA, Nam Y, Haerty W, Simpson GG, Akay A. U6 snRNA m6A modification is required for accurate and efficient cis- and trans-splicing of C. elegans mRNAs. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.09.16.558044. [PMID: 37745402 PMCID: PMC10516052 DOI: 10.1101/2023.09.16.558044] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/26/2023]
Abstract
pre-mRNA splicing is a critical feature of eukaryotic gene expression. Many eukaryotes use cis-splicing to remove intronic sequences from pre-mRNAs. In addition to cis-splicing, many organisms use trans-splicing to replace the 5' ends of mRNAs with a non-coding spliced-leader RNA. Both cis- and trans-splicing rely on accurately recognising splice site sequences by spliceosomal U snRNAs and associated proteins. Spliceosomal snRNAs carry multiple RNA modifications with the potential to affect different stages of pre-mRNA splicing. Here, we show that m6A modification of U6 snRNA A43 by the RNA methyltransferase METT-10 is required for accurate and efficient cis- and trans-splicing of C. elegans pre-mRNAs. The absence of U6 snRNA m6A modification primarily leads to alternative splicing at 5' splice sites. Furthermore, weaker 5' splice site recognition by the unmodified U6 snRNA A43 affects splicing at 3' splice sites. U6 snRNA m6A43 and the splicing factor SNRNP27K function to recognise an overlapping set of 5' splice sites with an adenosine at +4 position. Finally, we show that U6 snRNA m6A43 is required for efficient SL trans-splicing at weak 3' trans-splice sites. We conclude that the U6 snRNA m6A modification is important for accurate and efficient cis- and trans-splicing in C. elegans.
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Affiliation(s)
- Aykut Shen
- School of Biological Sciences, University of East Anglia, NR4 7TJ, Norwich
| | - Katarzyna Hencel
- School of Biological Sciences, University of East Anglia, NR4 7TJ, Norwich
- These authors contributed equally
| | - Matthew T Parker
- School of Life Sciences, University of Dundee, Dow Street, Dundee, DD1 5EH, UK
- These authors contributed equally
| | - Robyn Scott
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Roberta Skukan
- School of Biological Sciences, University of East Anglia, NR4 7TJ, Norwich
| | | | | | - Eric A Miska
- Wellcome/CRUK Gurdon Institute, University of Cambridge, Tennis Court Rd, Cambridge, CB2 1QN, UK
| | - Yunsun Nam
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX, USA
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA
- Simmons Comprehensive Cancer Center, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Wilfried Haerty
- School of Biological Sciences, University of East Anglia, NR4 7TJ, Norwich
- Earlham Institute, Norwich Research Park, Norwich, UK
| | - Gordon G Simpson
- School of Life Sciences, University of Dundee, Dow Street, Dundee, DD1 5EH, UK
- Cell & Molecular Sciences, James Hutton Institute, Invergowrie, DD2 5DA, UK
| | - Alper Akay
- School of Biological Sciences, University of East Anglia, NR4 7TJ, Norwich
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5
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Neugroschl A, Catrina IE. TFOFinder: Python program for identifying purine-only double-stranded stretches in the predicted secondary structure(s) of RNA targets. PLoS Comput Biol 2023; 19:e1011418. [PMID: 37624852 PMCID: PMC10484449 DOI: 10.1371/journal.pcbi.1011418] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2023] [Revised: 09/07/2023] [Accepted: 08/08/2023] [Indexed: 08/27/2023] Open
Abstract
Nucleic acid probes are valuable tools in biology and chemistry and are indispensable for PCR amplification of DNA, RNA quantification and visualization, and downregulation of gene expression. Recently, triplex-forming oligonucleotides (TFO) have received increased attention due to their improved selectivity and sensitivity in recognizing purine-rich double-stranded RNA regions at physiological pH by incorporating backbone and base modifications. For example, triplex-forming peptide nucleic acid (PNA) oligomers have been used for imaging a structured RNA in cells and inhibiting influenza A replication. Although a handful of programs are available to identify triplex target sites (TTS) in DNA, none are available that find such regions in structured RNAs. Here, we describe TFOFinder, a Python program that facilitates the identification of intramolecular purine-only RNA duplexes that are amenable to forming parallel triple helices (pyrimidine/purine/pyrimidine) and the design of the corresponding TFO(s). We performed genome- and transcriptome-wide analyses of TTS in Drosophila melanogaster and found that only 0.3% (123) of total unique transcripts (35,642) show the potential of forming 12-purine long triplex forming sites that contain at least one guanine. Using minimization algorithms, we predicted the secondary structure(s) of these transcripts, and using TFOFinder, we found that 97 (79%) of the identified 123 transcripts are predicted to fold to form at least one TTS for parallel triple helix formation. The number of transcripts with potential purine TTS increases when the strict search conditions are relaxed by decreasing the length of the probe or by allowing up to two pyrimidine inversions or 1-nucleotide bulge in the target site. These results are encouraging for the use of modified triplex forming probes for live imaging of endogenous structured RNA targets, such as pre-miRNAs, and inhibition of target-specific translation and viral replication.
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Affiliation(s)
- Atara Neugroschl
- Department of Chemistry and Biochemistry, Stern College for Women, Yeshiva University, New York, New York, United States of America
| | - Irina E. Catrina
- Department of Chemistry and Biochemistry, Yeshiva College, Yeshiva University, New York, New York, United States of America
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6
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Chung K, Xu L, Chai P, Peng J, Devarkar SC, Pyle AM. Structures of a mobile intron retroelement poised to attack its structured DNA target. Science 2022; 378:627-634. [PMID: 36356138 PMCID: PMC10190682 DOI: 10.1126/science.abq2844] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Group II introns are ribozymes that catalyze their self-excision and function as retroelements that invade DNA. As retrotransposons, group II introns form ribonucleoprotein (RNP) complexes that roam the genome, integrating by reversal of forward splicing. Here we show that retrotransposition is achieved by a tertiary complex between a structurally elaborate ribozyme, its protein mobility factor, and a structured DNA substrate. We solved cryo-electron microscopy structures of an intact group IIC intron-maturase retroelement that was poised for integration into a DNA stem-loop motif. By visualizing the RNP before and after DNA targeting, we show that it is primed for attack and fits perfectly with its DNA target. This study reveals design principles of a prototypical retroelement and reinforces the hypothesis that group II introns are ancient elements of genetic diversification.
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Affiliation(s)
- Kevin Chung
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06511, USA
| | - Ling Xu
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06511 USA
- Howard Hughes Medical Institute, Chevy Chase, MD 20815, USA
| | - Pengxin Chai
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06511, USA
| | - Junhui Peng
- Laboratory of Evolutionary Genetics and Genomics, The Rockefeller University, New York, NY 10065, USA
| | - Swapnil C. Devarkar
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06511, USA
| | - Anna Marie Pyle
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06511 USA
- Howard Hughes Medical Institute, Chevy Chase, MD 20815, USA
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7
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Abstract
Recent events have pushed RNA research into the spotlight. Continued discoveries of RNA with unexpected diverse functions in healthy and diseased cells, such as the role of RNA as both the source and countermeasure to a severe acute respiratory syndrome coronavirus 2 infection, are igniting a new passion for understanding this functionally and structurally versatile molecule. Although RNA structure is key to function, many foundational characteristics of RNA structure are misunderstood, and the default state of RNA is often thought of and depicted as a single floppy strand. The purpose of this perspective is to help adjust mental models, equipping the community to better use the fundamental aspects of RNA structural information in new mechanistic models, enhance experimental design to test these models, and refine data interpretation. We discuss six core observations focused on the inherent nature of RNA structure and how to incorporate these characteristics to better understand RNA structure. We also offer some ideas for future efforts to make validated RNA structural information available and readily used by all researchers.
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Affiliation(s)
- Quentin Vicens
- Department of Biochemistry and Molecular Genetics, University of Colorado Anschutz Medical Campus, School of Medicine, Aurora, CO 80045
- RNA BioScience Initiative, University of Colorado Denver School of Medicine, Aurora, CO 80045
| | - Jeffrey S. Kieft
- Department of Biochemistry and Molecular Genetics, University of Colorado Anschutz Medical Campus, School of Medicine, Aurora, CO 80045
- RNA BioScience Initiative, University of Colorado Denver School of Medicine, Aurora, CO 80045
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8
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El Fatimy R, Zhang Y, Deforzh E, Ramadas M, Saravanan H, Wei Z, Rabinovsky R, Teplyuk NM, Uhlmann EJ, Krichevsky AM. A nuclear function for an oncogenic microRNA as a modulator of snRNA and splicing. Mol Cancer 2022; 21:17. [PMID: 35033060 PMCID: PMC8760648 DOI: 10.1186/s12943-022-01494-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2021] [Accepted: 12/23/2021] [Indexed: 01/09/2023] Open
Abstract
BACKGROUND miRNAs are regulatory transcripts established as repressors of mRNA stability and translation that have been functionally implicated in carcinogenesis. miR-10b is one of the key onco-miRs associated with multiple forms of cancer. Malignant gliomas exhibit particularly striking dependence on miR-10b. However, despite the therapeutic potential of miR-10b targeting, this miRNA's poorly investigated and largely unconventional properties hamper the clinical translation. METHODS We utilized Covalent Ligation of Endogenous Argonaute-bound RNAs and their high-throughput RNA sequencing to identify miR-10b interactome and a combination of biochemical and imaging approaches for target validation. They included Crosslinking and RNA immunoprecipitation with spliceosomal proteins, a combination of miRNA FISH with protein immunofluorescence in glioma cells and patient-derived tumors, native Northern blotting, and the transcriptome-wide analysis of alternative splicing. RESULTS We demonstrate that miR-10b binds to U6 snRNA, a core component of the spliceosomal machinery. We provide evidence of the direct binding between miR-10b and U6, in situ imaging of miR-10b and U6 co-localization in glioma cells and tumors, and biochemical co-isolation of miR-10b with the components of the spliceosome. We further demonstrate that miR-10b modulates U6 N-6-adenosine methylation and pseudouridylation, U6 binding to splicing factors SART3 and PRPF8, and regulates U6 stability, conformation, and levels. These effects on U6 result in global splicing alterations, exemplified by the altered ratio of the isoforms of a small GTPase CDC42, reduced overall CDC42 levels, and downstream CDC42 -mediated effects on cell viability. CONCLUSIONS We identified U6 snRNA, the key RNA component of the spliceosome, as the top miR-10b target in glioblastoma. We, therefore, present an unexpected intersection of the miRNA and splicing machineries and a new nuclear function for a major cancer-associated miRNA.
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Affiliation(s)
- Rachid El Fatimy
- Department of Neurology, Brigham and Women's Hospital and Harvard Medical School, 60 Fenwood Rd, Room 9002T, Boston, MA, 02115, USA
- Current Address: Institute of Biological Sciences (ISSB-P), Mohammed VI Polytechnic University (UM6P), 43150, Benguerir, Morocco
| | - Yanhong Zhang
- Department of Neurology, Brigham and Women's Hospital and Harvard Medical School, 60 Fenwood Rd, Room 9002T, Boston, MA, 02115, USA
| | - Evgeny Deforzh
- Department of Neurology, Brigham and Women's Hospital and Harvard Medical School, 60 Fenwood Rd, Room 9002T, Boston, MA, 02115, USA
| | - Mahalakshmi Ramadas
- Department of Neurology, Brigham and Women's Hospital and Harvard Medical School, 60 Fenwood Rd, Room 9002T, Boston, MA, 02115, USA
| | - Harini Saravanan
- Department of Neurology, Brigham and Women's Hospital and Harvard Medical School, 60 Fenwood Rd, Room 9002T, Boston, MA, 02115, USA
| | - Zhiyun Wei
- Department of Neurology, Brigham and Women's Hospital and Harvard Medical School, 60 Fenwood Rd, Room 9002T, Boston, MA, 02115, USA
- Current Address: Shanghai Key Laboratory of Maternal Fetal Medicine, Shanghai First Maternity and Infant Hospital, School of Medicine, Tongji University, Shanghai, 200092, China
| | - Rosalia Rabinovsky
- Department of Neurology, Brigham and Women's Hospital and Harvard Medical School, 60 Fenwood Rd, Room 9002T, Boston, MA, 02115, USA
| | - Nadiya M Teplyuk
- Department of Neurology, Brigham and Women's Hospital and Harvard Medical School, 60 Fenwood Rd, Room 9002T, Boston, MA, 02115, USA
| | - Erik J Uhlmann
- Department of Neurology, Brigham and Women's Hospital and Harvard Medical School, 60 Fenwood Rd, Room 9002T, Boston, MA, 02115, USA
| | - Anna M Krichevsky
- Department of Neurology, Brigham and Women's Hospital and Harvard Medical School, 60 Fenwood Rd, Room 9002T, Boston, MA, 02115, USA.
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9
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Marcia M, Manigrasso J, De Vivo M. Finding the Ion in the RNA-Stack: Can Computational Models Accurately Predict Key Functional Elements in Large Macromolecular Complexes? J Chem Inf Model 2021; 61:2511-2515. [PMID: 34133879 PMCID: PMC8278382 DOI: 10.1021/acs.jcim.1c00572] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
This viewpoint discusses the predictive power and impact of computational analyses and simulations to gain prospective, experimentally supported mechanistic insights into complex biological systems. Remarkably, two newly resolved cryoEM structures have confirmed the previous, and independent, prediction of the precise localization and dynamics of key catalytic ions in megadalton-large spliceosomal complexes. This outstanding outcome endorses a prominent synergy of computational and experimental methods in the prospective exploration of such large multicomponent biosystems.
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Affiliation(s)
- Marco Marcia
- European Molecular Biology Laboratory (EMBL) Grenoble, 71 Avenue des Martyrs, Grenoble 38042, France
| | - Jacopo Manigrasso
- Laboratory of Molecular Modelling & Drug Discovery, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genoa, Italy
| | - Marco De Vivo
- Laboratory of Molecular Modelling & Drug Discovery, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genoa, Italy
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10
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Wilkinson ME, Fica SM, Galej WP, Nagai K. Structural basis for conformational equilibrium of the catalytic spliceosome. Mol Cell 2021; 81:1439-1452.e9. [PMID: 33705709 PMCID: PMC8022279 DOI: 10.1016/j.molcel.2021.02.021] [Citation(s) in RCA: 28] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2020] [Revised: 12/14/2020] [Accepted: 02/11/2021] [Indexed: 12/21/2022]
Abstract
The ATPase Prp16 governs equilibrium between the branching (B∗/C) and exon ligation (C∗/P) conformations of the spliceosome. Here, we present the electron cryomicroscopy reconstruction of the Saccharomyces cerevisiae C-complex spliceosome at 2.8 Å resolution and identify a novel C-complex intermediate (Ci) that elucidates the molecular basis for this equilibrium. The exon-ligation factors Prp18 and Slu7 bind to Ci before ATP hydrolysis by Prp16 can destabilize the branching conformation. Biochemical assays suggest that these pre-bound factors prime the C complex for conversion to C∗ by Prp16. A complete model of the Prp19 complex (NTC) reveals how the branching factors Yju2 and Isy1 are recruited by the NTC before branching. Prp16 remodels Yju2 binding after branching, allowing Yju2 to remain tethered to the NTC in the C∗ complex to promote exon ligation. Our results explain how Prp16 action modulates the dynamic binding of step-specific factors to alternatively stabilize the C or C∗ conformation and establish equilibrium of the catalytic spliceosome. Cryo-EM reveals new Ci spliceosome intermediate between branching and exon ligation Binding of branching and exon-ligation factors to Ci governs spliceosome equilibrium Exon-ligation factors Slu7 and Prp18 bind Ci weakly before Prp16 action After Prp16 action, pre-bound Slu7 and Prp18 bind strongly to promote exon ligation
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Affiliation(s)
- Max E Wilkinson
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge Biomedical Campus, Cambridge CB2 0QH, UK.
| | - Sebastian M Fica
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge Biomedical Campus, Cambridge CB2 0QH, UK.
| | - Wojciech P Galej
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge Biomedical Campus, Cambridge CB2 0QH, UK
| | - Kiyoshi Nagai
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge Biomedical Campus, Cambridge CB2 0QH, UK
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11
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Arabidopsis Mitochondrial Transcription Termination Factor mTERF2 Promotes Splicing of Group IIB Introns. Cells 2021; 10:cells10020315. [PMID: 33546419 PMCID: PMC7913559 DOI: 10.3390/cells10020315] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Revised: 01/29/2021] [Accepted: 01/30/2021] [Indexed: 12/21/2022] Open
Abstract
Plastid gene expression (PGE) is essential for chloroplast biogenesis and function and, hence, for plant development. However, many aspects of PGE remain obscure due to the complexity of the process. A hallmark of nuclear-organellar coordination of gene expression is the emergence of nucleus-encoded protein families, including nucleic-acid binding proteins, during the evolution of the green plant lineage. One of these is the mitochondrial transcription termination factor (mTERF) family, the members of which regulate various steps in gene expression in chloroplasts and/or mitochondria. Here, we describe the molecular function of the chloroplast-localized mTERF2 in Arabidopsis thaliana. The complete loss of mTERF2 function results in embryo lethality, whereas directed, microRNA (amiR)-mediated knockdown of MTERF2 is associated with perturbed plant development and reduced chlorophyll content. Moreover, photosynthesis is impaired in amiR-mterf2 plants, as indicated by reduced levels of photosystem subunits, although the levels of the corresponding messenger RNAs are not affected. RNA immunoprecipitation followed by RNA sequencing (RIP-Seq) experiments, combined with whole-genome RNA-Seq, RNA gel-blot, and quantitative RT-PCR analyses, revealed that mTERF2 is required for the splicing of the group IIB introns of ycf3 (intron 1) and rps12.
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12
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Kück U, Schmitt O. The Chloroplast Trans-Splicing RNA-Protein Supercomplex from the Green Alga Chlamydomonas reinhardtii. Cells 2021; 10:cells10020290. [PMID: 33535503 PMCID: PMC7912774 DOI: 10.3390/cells10020290] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2020] [Revised: 01/18/2021] [Accepted: 01/20/2021] [Indexed: 12/27/2022] Open
Abstract
In eukaryotes, RNA trans-splicing is a significant RNA modification process for the end-to-end ligation of exons from separately transcribed primary transcripts to generate mature mRNA. So far, three different categories of RNA trans-splicing have been found in organisms within a diverse range. Here, we review trans-splicing of discontinuous group II introns, which occurs in chloroplasts and mitochondria of lower eukaryotes and plants. We discuss the origin of intronic sequences and the evolutionary relationship between chloroplast ribonucleoprotein complexes and the nuclear spliceosome. Finally, we focus on the ribonucleoprotein supercomplex involved in trans-splicing of chloroplast group II introns from the green alga Chlamydomonas reinhardtii. This complex has been well characterized genetically and biochemically, resulting in a detailed picture of the chloroplast ribonucleoprotein supercomplex. This information contributes substantially to our understanding of the function of RNA-processing machineries and might provide a blueprint for other splicing complexes involved in trans- as well as cis-splicing of organellar intron RNAs.
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13
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Bai R, Wan R, Yan C, Jia Q, Lei J, Shi Y. Mechanism of spliceosome remodeling by the ATPase/helicase Prp2 and its coactivator Spp2. Science 2020; 371:science.abe8863. [PMID: 33243853 DOI: 10.1126/science.abe8863] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2020] [Accepted: 11/04/2020] [Indexed: 01/01/2023]
Abstract
Spliceosome remodeling, executed by conserved adenosine triphosphatase (ATPase)/helicases including Prp2, enables precursor messenger RNA (pre-mRNA) splicing. However, the structural basis for the function of the ATPase/helicases remains poorly understood. Here, we report atomic structures of Prp2 in isolation, Prp2 complexed with its coactivator Spp2, and Prp2-loaded activated spliceosome and the results of structure-guided biochemical analysis. Prp2 weakly associates with the spliceosome and cannot function without Spp2, which stably associates with Prp2 and anchors on the spliceosome, thus tethering Prp2 to the activated spliceosome and allowing Prp2 to function. Pre-mRNA is loaded into a featured channel between the N and C halves of Prp2, where Leu536 from the N half and Arg844 from the C half prevent backward sliding of pre-mRNA toward its 5'-end. Adenosine 5'-triphosphate binding and hydrolysis trigger interdomain movement in Prp2, which drives unidirectional stepwise translocation of pre-mRNA toward its 3'-end. These conserved mechanisms explain the coupling of spliceosome remodeling to pre-mRNA splicing.
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Affiliation(s)
- Rui Bai
- Key Laboratory of Structural Biology of Zhejiang Province, School of Life Sciences, Westlake University, Hangzhou 310024, Zhejiang Province, China.,Westlake Laboratory of Life Sciences and Biomedicine, Xihu District, Hangzhou 310024, Zhejiang Province, China.,Institute of Biology, Westlake Institute for Advanced Study, 18 Shilongshan Road, Xihu District, Hangzhou 310024, Zhejiang Province, China
| | - Ruixue Wan
- Key Laboratory of Structural Biology of Zhejiang Province, School of Life Sciences, Westlake University, Hangzhou 310024, Zhejiang Province, China. .,Westlake Laboratory of Life Sciences and Biomedicine, Xihu District, Hangzhou 310024, Zhejiang Province, China.,Institute of Biology, Westlake Institute for Advanced Study, 18 Shilongshan Road, Xihu District, Hangzhou 310024, Zhejiang Province, China
| | - Chuangye Yan
- Beijing Advanced Innovation Center for Structural Biology and Advanced Research Center for Biological Structure, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Qi Jia
- Beijing Advanced Innovation Center for Structural Biology and Advanced Research Center for Biological Structure, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Jianlin Lei
- Beijing Advanced Innovation Center for Structural Biology and Advanced Research Center for Biological Structure, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China.,Technology Center for Protein Sciences, Ministry of Education Key Laboratory of Protein Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Yigong Shi
- Key Laboratory of Structural Biology of Zhejiang Province, School of Life Sciences, Westlake University, Hangzhou 310024, Zhejiang Province, China. .,Westlake Laboratory of Life Sciences and Biomedicine, Xihu District, Hangzhou 310024, Zhejiang Province, China.,Institute of Biology, Westlake Institute for Advanced Study, 18 Shilongshan Road, Xihu District, Hangzhou 310024, Zhejiang Province, China.,Beijing Advanced Innovation Center for Structural Biology and Advanced Research Center for Biological Structure, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China
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14
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Malina J, Farrell NP, Brabec V. Substitution-Inert Polynuclear Platinum Complexes Inhibit Reverse Transcription Preferentially in RNA Triplex-Forming Templates. Inorg Chem 2020; 59:15135-15143. [PMID: 32988198 DOI: 10.1021/acs.inorgchem.0c02070] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
RNA triplexes are significant tertiary structure motifs that are found in many functional RNAs. Hence, small molecules capable of recognition, binding, and stabilization of the triple-helical RNA structures are emerging as attractive potential molecular biology tools and therapeutic agents. Here, we utilize methods of molecular biology and biophysics to study the interactions of a series of antitumor substitution-inert polynuclear platinum complexes (SI-PPCs) with triple-helical RNA structures. We show that SI-PPCs recognize and stabilize RNA triplexes and inhibit reverse transcription preferentially in the RNA template prone to the triplex formation. These so far unexplored properties of SI-PPCs suggest that the targeting of triple-stranded regions in RNA might contribute to the biological effects of SI-PPCs.
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Affiliation(s)
- Jaroslav Malina
- Czech Academy of Sciences, Institute of Biophysics, Kralovopolska 135, Brno CZ-61265, Czech Republic
| | - Nicholas P Farrell
- Department of Chemistry, Virginia Commonwealth University, Richmond, Virginia 23284-2006, United States
| | - Viktor Brabec
- Czech Academy of Sciences, Institute of Biophysics, Kralovopolska 135, Brno CZ-61265, Czech Republic
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15
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Ciavarella J, Perea W, Greenbaum NL. Topology of the U12-U6 atac snRNA Complex of the Minor Spliceosome and Binding by NTC-Related Protein RBM22. ACS OMEGA 2020; 5:23549-23558. [PMID: 32984674 PMCID: PMC7512442 DOI: 10.1021/acsomega.0c01674] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2020] [Accepted: 08/04/2020] [Indexed: 06/02/2023]
Abstract
Splicing of precursor messenger RNA is catalyzed by the spliceosome, a dynamic ribonucleoprotein assembly including five small nuclear (sn)RNAs and >100 proteins. RNA components catalyze the two transesterification reactions, but proteins perform critical roles in assembly and rearrangement. The catalytic core comprises a paired complex of U2 and U6 snRNAs for the major form of the spliceosome and U12 and U6atac snRNAs for the minor variant (∼0.3% of all spliceosomes in higher eukaryotes); the latter shares key catalytic sequence elements and performs identical chemistry. Here we use solution NMR techniques to show that the U12-U6atac snRNA complex of both human and Arabidopsis maintain base-pairing patterns similar to those in the three-helix model of the U2-U6 snRNA complex that position key elements to form the spliceosome's active site. However, in place of the stacked base pairs at the base of the U6 snRNA intramolecular stem loop and the central junction of the U2-U6 snRNA complex, we see altered geometry in the single-stranded hinge region opposing termini of the snRNAs to enable interaction between the key elements. We then use electrophoretic mobility shift assays and fluorescence assays to show that the protein RBM22, implicated in remodeling the human U2-U6 snRNA complex prior to catalysis, also binds the U12-U6atac snRNA complexes specifically and with similar affinity as to U2-U6 snRNA (a mean K d for the two methods = 3.4 and 8.0 μM for U2-U6 and U12-U6atac snRNA complexes, respectively), suggesting that RBM22 performs the same role in both spliceosomes.
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Affiliation(s)
- Joanna Ciavarella
- Ph.D.
Program in Chemistry, The Graduate Center
of the City University of New York, New York, New York 10016, United States
- Department
of Chemistry, Hunter College of the City
University of New York, New York, New York 10065, United States
| | - William Perea
- Department
of Chemistry, Hunter College of the City
University of New York, New York, New York 10065, United States
| | - Nancy L. Greenbaum
- Ph.D.
Program in Chemistry, The Graduate Center
of the City University of New York, New York, New York 10016, United States
- Ph.D.
Program in Biochemistry, The Graduate Center
of the City University of New York, New York, New York 10016, United States
- Department
of Chemistry, Hunter College of the City
University of New York, New York, New York 10065, United States
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16
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Fica SM. Cryo-EM snapshots of the human spliceosome reveal structural adaptions for splicing regulation. Curr Opin Struct Biol 2020; 65:139-148. [PMID: 32717639 DOI: 10.1016/j.sbi.2020.06.018] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2020] [Revised: 06/19/2020] [Accepted: 06/21/2020] [Indexed: 12/28/2022]
Abstract
Introns are excised from pre-messenger RNAs by the spliceosome, which produces mRNAs with continuous protein-coding information. In humans, most pre-mRNAs undergo alternative splicing to expand proteomic diversity. Cryo-electron microscopy (cryo-EM) structures of the yeast spliceosome elucidated how proteins stabilize and remodel an RNA-based active site to effect splicing catalysis. More recent cryo-EM snapshots of the human spliceosome reveal a complex protein scaffold and provide insights into the role of specific human proteins in modulating spliceosome activation, splice site positioning, and the ATPase-mediated dynamics of the active site. The emerging molecular picture highlights how, compared to its yeast counterpart, the human spliceosome has coopted additional protein factors to allow increased plasticity of splice site recognition and remodeling, and potentially to regulate alternative splicing.
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Affiliation(s)
- Sebastian M Fica
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, United Kingdom.
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17
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Chu H, Perea W, Greenbaum NL. Role of the central junction in folding topology of the protein-free human U2-U6 snRNA complex. RNA (NEW YORK, N.Y.) 2020; 26:836-850. [PMID: 32220895 PMCID: PMC7297123 DOI: 10.1261/rna.073379.119] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2019] [Accepted: 03/16/2020] [Indexed: 06/02/2023]
Abstract
U2 and U6 small nuclear (sn)RNAs are the only snRNAs directly implicated in catalyzing the splicing of pre-mRNA, but assembly and rearrangement steps prior to catalysis require numerous proteins. Previous studies have shown that the protein-free U2-U6 snRNA complex adopts two conformations in equilibrium, characterized by four and three helices surrounding a central junction. The four-helix conformer is strongly favored in the in vitro protein-free state, but the three-helix conformer predominates in spliceosomes. To analyze the role of the central junction in positioning elements forming the active site, we derived three-dimensional models of the two conformations from distances measured between fluorophores at selected locations in constructs representing the protein-free human U2-U6 snRNA complex by time-resolved fluorescence resonance energy transfer. Data describing four angles in the four-helix conformer suggest tetrahedral geometry; addition of Mg2+ results in shortening of the distances between neighboring helices, indicating compaction of the complex around the junction. In contrast, the three-helix conformer shows a closer approach between helices bearing critical elements, but the addition of Mg2+ widens the distance between them; thus in neither conformer are the critical helices positioned to favor the proposed triplex interaction. The presence of Mg2+ also enhances the fraction of the three-helix conformer, as does incubation with the Prp19-related protein RBM22, which has been implicated in the remodeling of the U2-U6 snRNA complex to render it catalytically active. These data suggest that although the central junction assumes a significant role in orienting helices, spliceosomal proteins and Mg2+ facilitate formation of the catalytically active conformer.
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Affiliation(s)
- Huong Chu
- Department of Chemistry, Hunter College of the City University of New York, New York, New York 10065, USA
- Ph.D. Program in Chemistry, The Graduate Center of the City University of New York, New York, New York 10016, USA
| | - William Perea
- Department of Chemistry, Hunter College of the City University of New York, New York, New York 10065, USA
| | - Nancy L Greenbaum
- Department of Chemistry, Hunter College of the City University of New York, New York, New York 10065, USA
- Ph.D. Program in Chemistry, The Graduate Center of the City University of New York, New York, New York 10016, USA
- Ph.D. Program in Biochemistry, The Graduate Center of the City University of New York, New York, New York 10016, USA
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18
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Abstract
Splicing of the precursor messenger RNA, involving intron removal and exon ligation, is mediated by the spliceosome. Together with biochemical and genetic investigations of the past four decades, structural studies of the intact spliceosome at atomic resolution since 2015 have led to mechanistic delineation of RNA splicing with remarkable insights. The spliceosome is proven to be a protein-orchestrated metalloribozyme. Conserved elements of small nuclear RNA (snRNA) constitute the splicing active site with two catalytic metal ions and recognize three conserved intron elements through duplex formation, which are delivered into the splicing active site for branching and exon ligation. The protein components of the spliceosome stabilize the conformation of the snRNA, drive spliceosome remodeling, orchestrate the movement of the RNA elements, and facilitate the splicing reaction. The overall organization of the spliceosome and the configuration of the splicing active site are strictly conserved between human and yeast.
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Affiliation(s)
- Ruixue Wan
- Beijing Advanced Innovation Center for Structural Biology, School of Life Sciences and School of Medicine, Tsinghua University, Beijing 100084, China;,
| | - Rui Bai
- Institute of Biology, Westlake Institute for Advanced Study, Westlake University, Hangzhou 310024, China
| | - Xiechao Zhan
- Beijing Advanced Innovation Center for Structural Biology, School of Life Sciences and School of Medicine, Tsinghua University, Beijing 100084, China;,
| | - Yigong Shi
- Beijing Advanced Innovation Center for Structural Biology, School of Life Sciences and School of Medicine, Tsinghua University, Beijing 100084, China;,
- Institute of Biology, Westlake Institute for Advanced Study, Westlake University, Hangzhou 310024, China
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19
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Brown JA. Unraveling the structure and biological functions of RNA triple helices. WILEY INTERDISCIPLINARY REVIEWS-RNA 2020; 11:e1598. [PMID: 32441456 PMCID: PMC7583470 DOI: 10.1002/wrna.1598] [Citation(s) in RCA: 35] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/18/2020] [Revised: 04/06/2020] [Accepted: 04/15/2020] [Indexed: 02/06/2023]
Abstract
It has been nearly 63 years since the first characterization of an RNA triple helix in vitro by Gary Felsenfeld, David Davies, and Alexander Rich. An RNA triple helix consists of three strands: A Watson–Crick RNA double helix whose major‐groove establishes hydrogen bonds with the so‐called “third strand”. In the past 15 years, it has been recognized that these major‐groove RNA triple helices, like single‐stranded and double‐stranded RNA, also mediate prominent biological roles inside cells. Thus far, these triple helices are known to mediate catalysis during telomere synthesis and RNA splicing, bind to ligands and ions so that metabolite‐sensing riboswitches can regulate gene expression, and provide a clever strategy to protect the 3′ end of RNA from degradation. Because RNA triple helices play important roles in biology, there is a renewed interest in better understanding the fundamental properties of RNA triple helices and developing methods for their high‐throughput discovery. This review provides an overview of the fundamental biochemical and structural properties of major‐groove RNA triple helices, summarizes the structure and function of naturally occurring RNA triple helices, and describes prospective strategies to isolate RNA triple helices as a means to establish the “triplexome”. This article is categorized under:RNA Structure and Dynamics > RNA Structure and Dynamics RNA Structure and Dynamics > RNA Structure, Dynamics and Chemistry RNA Structure and Dynamics > Influence of RNA Structure in Biological Systems
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Affiliation(s)
- Jessica A Brown
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana, USA
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20
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Haack DB, Toor N. Retroelement origins of pre-mRNA splicing. WILEY INTERDISCIPLINARY REVIEWS-RNA 2020; 11:e1589. [PMID: 32045511 DOI: 10.1002/wrna.1589] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/18/2019] [Revised: 01/22/2020] [Accepted: 01/23/2020] [Indexed: 12/22/2022]
Abstract
Recent cryo-EM structures of a group II intron caught in the process of invading DNA have given new insight into the mechanisms of both splicing and retrotransposition. Conformational dynamics involving the branch-site helix domain VI are responsible for substrate exchange between the two steps of splicing. These structural rearrangements have strong parallels with the movement of the branch-site helix in the spliceosome during catalysis. This is strong evidence for the spliceosome evolving from a group II intron ancestor. We observe other topological changes in the overall structure of the catalytic domain V that may occur in the spliceosome as well. Therefore, studying group II introns not only provides us with insight into the evolutionary origins of the spliceosome, but also may inform the design of experiments to further probe structure-function relationships in this eukaryotic splicing apparatus. This article is categorized under: RNA Processing > Splicing Mechanisms RNA Structure and Dynamics > RNA Structure, Dynamics, and Chemistry RNA Structure and Dynamics > Influence of RNA Structure in Biological Systems RNA Evolution and Genomics > RNA and Ribonucleoprotein Evolution.
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Affiliation(s)
- Daniel B Haack
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California
| | - Navtej Toor
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California
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21
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Abstract
The spliceosome removes introns from messenger RNA precursors (pre-mRNA). Decades of biochemistry and genetics combined with recent structural studies of the spliceosome have produced a detailed view of the mechanism of splicing. In this review, we aim to make this mechanism understandable and provide several videos of the spliceosome in action to illustrate the intricate choreography of splicing. The U1 and U2 small nuclear ribonucleoproteins (snRNPs) mark an intron and recruit the U4/U6.U5 tri-snRNP. Transfer of the 5' splice site (5'SS) from U1 to U6 snRNA triggers unwinding of U6 snRNA from U4 snRNA. U6 folds with U2 snRNA into an RNA-based active site that positions the 5'SS at two catalytic metal ions. The branch point (BP) adenosine attacks the 5'SS, producing a free 5' exon. Removal of the BP adenosine from the active site allows the 3'SS to bind, so that the 5' exon attacks the 3'SS to produce mature mRNA and an excised lariat intron.
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Affiliation(s)
- Max E Wilkinson
- MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom; ,
| | - Clément Charenton
- MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom; ,
| | - Kiyoshi Nagai
- MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom; ,
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22
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van der Feltz C, Hoskins AA. Structural and functional modularity of the U2 snRNP in pre-mRNA splicing. Crit Rev Biochem Mol Biol 2019; 54:443-465. [PMID: 31744343 DOI: 10.1080/10409238.2019.1691497] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The U2 small nuclear ribonucleoprotein (snRNP) is an essential component of the spliceosome, the cellular machine responsible for removing introns from precursor mRNAs (pre-mRNAs) in all eukaryotes. U2 is an extraordinarily dynamic splicing factor and the most frequently mutated in cancers. Cryo-electron microscopy (cryo-EM) has transformed our structural and functional understanding of the role of U2 in splicing. In this review, we synthesize these and other data with respect to a view of U2 as an assembly of interconnected functional modules. These modules are organized by the U2 small nuclear RNA (snRNA) for roles in spliceosome assembly, intron substrate recognition, and protein scaffolding. We describe new discoveries regarding the structure of U2 components and how the snRNP undergoes numerous conformational and compositional changes during splicing. We specifically highlight large scale movements of U2 modules as the spliceosome creates and rearranges its active site. U2 serves as a compelling example for how cellular machines can exploit the modular organization and structural plasticity of an RNP.
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Affiliation(s)
| | - Aaron A Hoskins
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI, USA
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23
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Kastner B, Will CL, Stark H, Lührmann R. Structural Insights into Nuclear pre-mRNA Splicing in Higher Eukaryotes. Cold Spring Harb Perspect Biol 2019; 11:cshperspect.a032417. [PMID: 30765414 DOI: 10.1101/cshperspect.a032417] [Citation(s) in RCA: 116] [Impact Index Per Article: 23.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The spliceosome is a highly complex, dynamic ribonucleoprotein molecular machine that undergoes numerous structural and compositional rearrangements that lead to the formation of its active site. Recent advances in cyroelectron microscopy (cryo-EM) have provided a plethora of near-atomic structural information about the inner workings of the spliceosome. Aided by previous biochemical, structural, and functional studies, cryo-EM has confirmed or provided a structural basis for most of the prevailing models of spliceosome function, but at the same time allowed novel insights into splicing catalysis and the intriguing dynamics of the spliceosome. The mechanism of pre-mRNA splicing is highly conserved between humans and yeast, but the compositional dynamics and ribonucleoprotein (RNP) remodeling of the human spliceosome are more complex. Here, we summarize recent advances in our understanding of the molecular architecture of the human spliceosome, highlighting differences between the human and yeast splicing machineries.
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Affiliation(s)
- Berthold Kastner
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, D-37077 Göttingen, Germany
| | - Cindy L Will
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, D-37077 Göttingen, Germany
| | - Holger Stark
- Department of Structural Dynamics, Max Planck Institute for Biophysical Chemistry, D-37077 Göttingen, Germany
| | - Reinhard Lührmann
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, D-37077 Göttingen, Germany
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24
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Toroney R, Nielsen KH, Staley JP. Termination of pre-mRNA splicing requires that the ATPase and RNA unwindase Prp43p acts on the catalytic snRNA U6. Genes Dev 2019; 33:1555-1574. [PMID: 31558568 PMCID: PMC6824469 DOI: 10.1101/gad.328294.119] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2019] [Accepted: 09/03/2019] [Indexed: 11/25/2022]
Abstract
In this study, Toroney et al. set out to identify the mechanism of Prp43p action in splicing. The authors use biochemical approaches to demonstrate that the 3' end of U6 acts as the key substrate by which Prp43p promotes disassembly and intron release, thereby terminating splicing. The termination of pre-mRNA splicing functions to discard suboptimal substrates, thereby enhancing fidelity, and to release excised introns in a manner coupled to spliceosome disassembly, thereby allowing recycling. The mechanism of termination, including the RNA target of the DEAH-box ATPase Prp43p, remains ambiguous. We discovered a critical role for nucleotides at the 3′ end of the catalytic U6 small nuclear RNA in splicing termination. Although conserved sequence at the 3′ end is not required, 2′ hydroxyls are, paralleling requirements for Prp43p biochemical activities. Although the 3′ end of U6 is not required for recruiting Prp43p to the spliceosome, the 3′ end cross-links directly to Prp43p in an RNA-dependent manner. Our data indicate a mechanism of splicing termination in which Prp43p translocates along U6 from the 3′ end to disassemble the spliceosome and thereby release suboptimal substrates or excised introns. This mechanism reveals that the spliceosome becomes primed for termination at the same stage it becomes activated for catalysis, implying a requirement for stringent control of spliceosome activity within the cell.
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Affiliation(s)
- Rebecca Toroney
- Department of Molecular Genetics and Cell Biology, University of Chicago, Illinois 60637, USA
| | - Klaus H Nielsen
- Department of Molecular Genetics and Cell Biology, University of Chicago, Illinois 60637, USA
| | - Jonathan P Staley
- Department of Molecular Genetics and Cell Biology, University of Chicago, Illinois 60637, USA
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25
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Daras G, Rigas S, Alatzas A, Samiotaki M, Chatzopoulos D, Tsitsekian D, Papadaki V, Templalexis D, Banilas G, Athanasiadou AM, Kostourou V, Panayotou G, Hatzopoulos P. LEFKOTHEA Regulates Nuclear and Chloroplast mRNA Splicing in Plants. Dev Cell 2019; 50:767-779.e7. [PMID: 31447263 DOI: 10.1016/j.devcel.2019.07.024] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2018] [Revised: 04/27/2019] [Accepted: 07/25/2019] [Indexed: 12/14/2022]
Abstract
Eukaryotic organisms accomplish the removal of introns to produce mature mRNAs through splicing. Nuclear and organelle splicing mechanisms are distinctively executed by spliceosome and group II intron complex, respectively. Here, we show that LEFKOTHEA, a nuclear encoded RNA-binding protein, participates in chloroplast group II intron and nuclear pre-mRNA splicing. Transiently optimized LEFKOTHEA nuclear activity is fundamental for plant growth, whereas the loss of function abruptly arrests embryogenesis. Nucleocytoplasmic partitioning and chloroplast allocation are efficiently balanced via functional motifs in LEFKOTHEA polypeptide. In the context of nuclear-chloroplast coevolution, our results provide a strong paradigm of the convergence of RNA maturation mechanisms in the nucleus and chloroplasts to coordinately regulate gene expression and effectively control plant growth.
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Affiliation(s)
- Gerasimos Daras
- Department of Biotechnology, Agricultural University of Athens, Athens, Greece
| | - Stamatis Rigas
- Department of Biotechnology, Agricultural University of Athens, Athens, Greece
| | - Anastasios Alatzas
- Department of Biotechnology, Agricultural University of Athens, Athens, Greece
| | - Martina Samiotaki
- Institute for Bioinnovation, Biomedical Sciences Research Center "Alexander Fleming", Athens, Greece
| | | | - Dikran Tsitsekian
- Department of Biotechnology, Agricultural University of Athens, Athens, Greece
| | - Vassiliki Papadaki
- Institute for Bioinnovation, Biomedical Sciences Research Center "Alexander Fleming", Athens, Greece
| | | | - Georgios Banilas
- Department of Biotechnology, Agricultural University of Athens, Athens, Greece
| | | | - Vassiliki Kostourou
- Institute for Bioinnovation, Biomedical Sciences Research Center "Alexander Fleming", Athens, Greece
| | - George Panayotou
- Institute for Bioinnovation, Biomedical Sciences Research Center "Alexander Fleming", Athens, Greece
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26
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Ageeli AA, McGovern-Gooch KR, Kaminska MM, Baird NJ. Finely tuned conformational dynamics regulate the protective function of the lncRNA MALAT1 triple helix. Nucleic Acids Res 2019; 47:1468-1481. [PMID: 30462290 PMCID: PMC6379651 DOI: 10.1093/nar/gky1171] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2018] [Revised: 10/28/2018] [Accepted: 11/03/2018] [Indexed: 12/21/2022] Open
Abstract
Nucleic acid triplexes may regulate many important biological processes. Persistent accumulation of the oncogenic 7-kb long noncoding RNA MALAT1 is dependent on an unusually long intramolecular triple helix. This triplex structure is positioned within a conserved ENE (element for nuclear expression) motif at the lncRNA 3′ terminus and protects the entire transcript from degradation in a polyA-independent manner. A requisite 3′ maturation step leads to triplex formation though the precise mechanism of triplex folding remains unclear. Furthermore, the contributions of several peripheral structural elements to triplex formation and protective function have not been determined. We evaluated the stability, conformational fluctuations, and function of this MALAT1 ENE triple helix (M1TH) protective element using in vitro mutational analyses coupled with biochemical and biophysical characterizations. Using fluorescence and UV melts, FRET, and an exonucleolytic decay assay we define a concerted mechanism for triplex formation and uncover a metastable, dynamic triplex population under near-physiological conditions. Structural elements surrounding the triplex regulate the dynamic M1TH conformational variability, but increased triplex dynamics lead to M1TH degradation. Taken together, we suggest that finely tuned dynamics may be a general mechanism regulating triplex-mediated functions.
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Affiliation(s)
- Abeer A Ageeli
- Department of Chemistry & Biochemistry, University of the Sciences, Philadelphia, PA 19143, USA
| | | | - Magdalena M Kaminska
- Department of Chemistry & Biochemistry, University of the Sciences, Philadelphia, PA 19143, USA
| | - Nathan J Baird
- Department of Chemistry & Biochemistry, University of the Sciences, Philadelphia, PA 19143, USA
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27
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Bao P, Boon KL, Will CL, Hartmuth K, Lührmann R. Multiple RNA-RNA tertiary interactions are dispensable for formation of a functional U2/U6 RNA catalytic core in the spliceosome. Nucleic Acids Res 2019; 46:12126-12138. [PMID: 30335160 PMCID: PMC6294511 DOI: 10.1093/nar/gky966] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Accepted: 10/05/2018] [Indexed: 01/24/2023] Open
Abstract
The active 3D conformation of the spliceosome's catalytic U2/U6 RNA core is stabilised by a network of secondary and tertiary RNA interactions, but also depends on spliceosomal proteins for its formation. To determine the contribution towards splicing of specific RNA secondary and tertiary interactions in the U2/U6 RNA core, we introduced mutations in critical U6 nucleotides and tested their effect on splicing using a yeast in vitro U6 depletion/complementation system. Elimination of selected RNA tertiary interactions involving the U6 catalytic triad, or deletions of the bases of U6-U80 or U6-A59, had moderate to no effect on splicing, showing that the affected secondary and tertiary interactions are not required for splicing catalysis. However, removal of the base of U6-G60 of the catalytic triad completely blocked splicing, without affecting assembly of the activated spliceosome or its subsequent conversion into a B*-like complex. Our data suggest that the catalytic configuration of the RNA core that allows catalytic metal M1 binding can be maintained by Protein–RNA contacts. However, RNA stacking interactions in the U2/U6 RNA core are required for productive coordination of metal M2. The functional conformation of the U2/U6 RNA core is thus highly buffered, with overlapping contributions from RNA–RNA and Protein–RNA interactions.
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Affiliation(s)
- Penghui Bao
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany
| | - Kum-Loong Boon
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany
| | - Cindy L Will
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany
| | - Klaus Hartmuth
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany
| | - Reinhard Lührmann
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany
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Eysmont K, Matylla-Kulińska K, Jaskulska A, Magnus M, Konarska MM. Rearrangements within the U6 snRNA Core during the Transition between the Two Catalytic Steps of Splicing. Mol Cell 2019; 75:538-548.e3. [PMID: 31229405 DOI: 10.1016/j.molcel.2019.05.018] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2019] [Revised: 04/10/2019] [Accepted: 05/12/2019] [Indexed: 12/20/2022]
Abstract
The RNA catalytic core of spliceosomes as visualized by cryoelectron microscopy (cryo-EM) remains unchanged at different stages of splicing. However, we demonstrate that mutations within the core of yeast U6 snRNA modulate conformational changes between the two catalytic steps. We propose that the intramolecular stem-loop (ISL) of U6 exists in two competing states, changing between a default, non-catalytic conformation and a transient, catalytic conformation. Whereas stable interactions in the catalytic triplex promote catalysis and their disruptions favor exit from the catalytic conformation, destabilization of the lower ISL stem promotes catalysis and its stabilization supports exit from the catalytic conformation. Thus, in addition to the catalytic triplex, U6-ISL acts as an important dynamic component of the catalytic center. The relative flexibility of the lower U6-ISL stem is conserved across eukaryotes. Similar features are found in U6atac and domain V of group II introns, arguing for the generality of the proposed mechanism.
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Affiliation(s)
- Katarzyna Eysmont
- Laboratory of RNA Biology, Centre of New Technologies, University of Warsaw, 02-097 Warsaw, Poland
| | | | - Agata Jaskulska
- Laboratory of RNA Biology, Centre of New Technologies, University of Warsaw, 02-097 Warsaw, Poland
| | - Marcin Magnus
- Laboratory of RNA Biology, Centre of New Technologies, University of Warsaw, 02-097 Warsaw, Poland; ReMedy-International Research Agenda Unit, Centre of New Technologies, University of Warsaw, 02-097 Warsaw, Poland
| | - Maria M Konarska
- Laboratory of RNA Biology, Centre of New Technologies, University of Warsaw, 02-097 Warsaw, Poland; ReMedy-International Research Agenda Unit, Centre of New Technologies, University of Warsaw, 02-097 Warsaw, Poland.
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29
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Smathers CM, Robart AR. The mechanism of splicing as told by group II introns: Ancestors of the spliceosome. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2019; 1862:194390. [PMID: 31202783 DOI: 10.1016/j.bbagrm.2019.06.001] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Accepted: 06/10/2019] [Indexed: 12/31/2022]
Abstract
Spliceosomal introns and self-splicing group II introns share a common mechanism of intron splicing where two sequential transesterification reactions remove intron lariats and ligate exons. The recent revolution in cryo-electron microscopy (cryo-EM) has allowed visualization of the spliceosome's ribozyme core. Comparison of these cryo-EM structures to recent group II intron crystal structures presents an opportunity to draw parallels between the RNA active site, substrate positioning, and product formation in these two model systems of intron splicing. In addition to shared RNA architectural features, structural similarity between group II intron encoded proteins (IEPs) and the integral spliceosomal protein Prp8 further support a shared catalytic core. These mechanistic and structural similarities support the long-held assertion that group II introns and the eukaryotic spliceosome have a common evolutionary origin. In this review, we discuss how recent structural insights into group II introns and the spliceosome facilitate the chemistry of splicing, highlight similarities between the two systems, and discuss their likely evolutionary connections. This article is part of a Special Issue entitled: RNA structure and splicing regulation edited by Francisco Baralle, Ravindra Singh and Stefan Stamm.
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Affiliation(s)
- Claire M Smathers
- Department of Biochemistry, West Virginia University, Morgantown, WV, United States of America
| | - Aaron R Robart
- Department of Biochemistry, West Virginia University, Morgantown, WV, United States of America.
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30
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Wan R, Bai R, Yan C, Lei J, Shi Y. Structures of the Catalytically Activated Yeast Spliceosome Reveal the Mechanism of Branching. Cell 2019; 177:339-351.e13. [PMID: 30879786 DOI: 10.1016/j.cell.2019.02.006] [Citation(s) in RCA: 52] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2018] [Revised: 12/10/2018] [Accepted: 02/06/2019] [Indexed: 11/17/2022]
Abstract
Pre-mRNA splicing is executed by the spliceosome. Structural characterization of the catalytically activated complex (B∗) is pivotal for understanding the branching reaction. In this study, we assembled the B∗ complexes on two different pre-mRNAs from Saccharomyces cerevisiae and determined the cryo-EM structures of four distinct B∗ complexes at overall resolutions of 2.9-3.8 Å. The duplex between U2 small nuclear RNA (snRNA) and the branch point sequence (BPS) is discretely away from the 5'-splice site (5'SS) in the three B∗ complexes that are devoid of the step I splicing factors Yju2 and Cwc25. Recruitment of Yju2 into the active site brings the U2/BPS duplex into the vicinity of 5'SS, with the BPS nucleophile positioned 4 Å away from the catalytic metal M2. This analysis reveals the functional mechanism of Yju2 and Cwc25 in branching. These structures on different pre-mRNAs reveal substrate-specific conformations of the spliceosome in a major functional state.
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Affiliation(s)
- Ruixue Wan
- Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences and School of Medicine, Tsinghua University, Beijing 100084, China
| | - Rui Bai
- Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences and School of Medicine, Tsinghua University, Beijing 100084, China
| | - Chuangye Yan
- Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences and School of Medicine, Tsinghua University, Beijing 100084, China
| | - Jianlin Lei
- Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences and School of Medicine, Tsinghua University, Beijing 100084, China; Technology Center for Protein Sciences, Ministry of Education Key Laboratory of Protein Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Yigong Shi
- Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences and School of Medicine, Tsinghua University, Beijing 100084, China; Institute of Biology, Westlake Institute for Advanced Study, School of Life Sciences, Westlake University, 18 Shilongshan Road, Xihu District, Hangzhou 310024, Zhejiang Province, China.
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31
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Fica SM, Oubridge C, Wilkinson ME, Newman AJ, Nagai K. A human postcatalytic spliceosome structure reveals essential roles of metazoan factors for exon ligation. Science 2019; 363:710-714. [PMID: 30705154 DOI: 10.1126/science.aaw5569] [Citation(s) in RCA: 66] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2019] [Accepted: 01/21/2019] [Indexed: 12/11/2022]
Abstract
During exon ligation, the Saccharomyces cerevisiae spliceosome recognizes the 3'-splice site (3'SS) of precursor messenger RNA (pre-mRNA) through non-Watson-Crick pairing with the 5'SS and the branch adenosine, in a conformation stabilized by Prp18 and Prp8. Here we present the 3.3-angstrom cryo-electron microscopy structure of a human postcatalytic spliceosome just after exon ligation. The 3'SS docks at the active site through conserved RNA interactions in the absence of Prp18. Unexpectedly, the metazoan-specific FAM32A directly bridges the 5'-exon and intron 3'SS of pre-mRNA and promotes exon ligation, as shown by functional assays. CACTIN, SDE2, and NKAP-factors implicated in alternative splicing-further stabilize the catalytic conformation of the spliceosome during exon ligation. Together these four proteins act as exon ligation factors. Our study reveals how the human spliceosome has co-opted additional proteins to modulate a conserved RNA-based mechanism for 3'SS selection and to potentially fine-tune alternative splicing at the exon ligation stage.
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Affiliation(s)
- Sebastian M Fica
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK.
| | - Chris Oubridge
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
| | - Max E Wilkinson
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
| | - Andrew J Newman
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
| | - Kiyoshi Nagai
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK.
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32
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Didychuk AL, Butcher SE, Brow DA. The life of U6 small nuclear RNA, from cradle to grave. RNA (NEW YORK, N.Y.) 2018; 24:437-460. [PMID: 29367453 PMCID: PMC5855946 DOI: 10.1261/rna.065136.117] [Citation(s) in RCA: 67] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Removal of introns from precursor messenger RNA (pre-mRNA) and some noncoding transcripts is an essential step in eukaryotic gene expression. In the nucleus, this process of RNA splicing is carried out by the spliceosome, a multi-megaDalton macromolecular machine whose core components are conserved from yeast to humans. In addition to many proteins, the spliceosome contains five uridine-rich small nuclear RNAs (snRNAs) that undergo an elaborate series of conformational changes to correctly recognize the splice sites and catalyze intron removal. Decades of biochemical and genetic data, along with recent cryo-EM structures, unequivocally demonstrate that U6 snRNA forms much of the catalytic core of the spliceosome and is highly dynamic, interacting with three snRNAs, the pre-mRNA substrate, and >25 protein partners throughout the splicing cycle. This review summarizes the current state of knowledge on how U6 snRNA is synthesized, modified, incorporated into snRNPs and spliceosomes, recycled, and degraded.
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Affiliation(s)
- Allison L Didychuk
- Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA
| | - Samuel E Butcher
- Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA
| | - David A Brow
- Department of Biomolecular Chemistry, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin 53706, USA
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33
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Galej WP, Toor N, Newman AJ, Nagai K. Molecular Mechanism and Evolution of Nuclear Pre-mRNA and Group II Intron Splicing: Insights from Cryo-Electron Microscopy Structures. Chem Rev 2018; 118:4156-4176. [PMID: 29377672 DOI: 10.1021/acs.chemrev.7b00499] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Nuclear pre-mRNA splicing and group II intron self-splicing both proceed by two-step transesterification reactions via a lariat intron intermediate. Recently determined cryo-electron microscopy (cryo-EM) structures of catalytically active spliceosomes revealed the RNA-based catalytic core and showed how pre-mRNA substrates and reaction products are positioned in the active site. These findings highlight a strong structural similarity to the group II intron active site, strengthening the notion that group II introns and spliceosomes evolved from a common ancestor. Prp8, the largest and most conserved protein in the spliceosome, cradles the active site RNA. Prp8 and group II intron maturase have a similar domain architecture, suggesting that they also share a common evolutionary origin. The interactions between maturase and key group II intron RNA elements, such as the exon-binding loop and domains V and VI, are recapitulated in the interactions between Prp8 and key elements in the spliceosome's catalytic RNA core. Structural comparisons suggest that the extensive RNA scaffold of the group II intron was gradually replaced by proteins as the spliceosome evolved. A plausible model of spliceosome evolution is discussed.
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Affiliation(s)
- Wojciech P Galej
- EMBL Grenoble , 71 Avenue des Martyrs , 38042 Grenoble Cedex 09 , France
| | - Navtej Toor
- Department of Chemistry and Biochemistry , University of California, San Diego , La Jolla , California 92093 , United States
| | - Andrew J Newman
- MRC Laboratory of Molecular Biology , Francis Crick Avenue , Cambridge CB2 0QH , U.K
| | - Kiyoshi Nagai
- MRC Laboratory of Molecular Biology , Francis Crick Avenue , Cambridge CB2 0QH , U.K
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34
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Haselbach D, Komarov I, Agafonov DE, Hartmuth K, Graf B, Dybkov O, Urlaub H, Kastner B, Lührmann R, Stark H. Structure and Conformational Dynamics of the Human Spliceosomal B act Complex. Cell 2018; 172:454-464.e11. [PMID: 29361316 DOI: 10.1016/j.cell.2018.01.010] [Citation(s) in RCA: 140] [Impact Index Per Article: 23.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2017] [Revised: 12/23/2017] [Accepted: 01/05/2018] [Indexed: 11/19/2022]
Abstract
The spliceosome is a highly dynamic macromolecular complex that precisely excises introns from pre-mRNA. Here we report the cryo-EM 3D structure of the human Bact spliceosome at 3.4 Å resolution. In the Bact state, the spliceosome is activated but not catalytically primed, so that it is functionally blocked prior to the first catalytic step of splicing. The spliceosomal core is similar to the yeast Bact spliceosome; important differences include the presence of the RNA helicase aquarius and peptidyl prolyl isomerases. To examine the overall dynamic behavior of the purified spliceosome, we developed a principal component analysis-based approach. Calculating the energy landscape revealed eight major conformational states, which we refined to higher resolution. Conformational differences of the highly flexible structural components between these eight states reveal how spliceosomal components contribute to the assembly of the spliceosome, allowing it to generate a dynamic interaction network required for its subsequent catalytic activation.
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Affiliation(s)
- David Haselbach
- Department for Structural Dynamics, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
| | - Ilya Komarov
- Department for Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
| | - Dmitry E Agafonov
- Department for Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
| | - Klaus Hartmuth
- Department for Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
| | - Benjamin Graf
- Department for Structural Dynamics, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
| | - Olexandr Dybkov
- Department for Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
| | - Henning Urlaub
- Bioanalytic Mass Spectrometry Group, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany; Bioanalytics Group, Institute for Clinical Chemistry, University Medical Center Göttingen, Robert-Koch-Str. 40, 37073 Göttingen, Germany
| | - Berthold Kastner
- Department for Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
| | - Reinhard Lührmann
- Department for Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany.
| | - Holger Stark
- Department for Structural Dynamics, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany.
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35
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Second-Shell Basic Residues Expand the Two-Metal-Ion Architecture of DNA and RNA Processing Enzymes. Structure 2017; 26:40-50.e2. [PMID: 29225080 PMCID: PMC5758106 DOI: 10.1016/j.str.2017.11.008] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2017] [Revised: 09/12/2017] [Accepted: 11/12/2017] [Indexed: 02/01/2023]
Abstract
Synthesis and scission of phosphodiester bonds in DNA and RNA regulate vital processes within the cell. Enzymes that catalyze these reactions operate mostly via the recognized two-metal-ion mechanism. Our analysis reveals that basic amino acids and monovalent cations occupy structurally conserved positions nearby the active site of many two-metal-ion enzymes for which high-resolution (<3 Å) structures are known, including DNA and RNA polymerases, nucleases such as Cas9, and splicing ribozymes. Integrating multiple-sequence and structural alignments with molecular dynamics simulations, electrostatic potential maps, and mutational data, we found that these elements always interact with the substrates, suggesting that they may play an active role for catalysis, in addition to their electrostatic contribution. We discuss possible mechanistic implications of this expanded two-metal-ion architecture, including inferences on medium-resolution cryoelectron microscopy structures. Ultimately, our analysis may inspire future experiments and strategies for enzyme engineering or drug design to modulate nucleic acid processing. Basic residues in the active site of two-metal-ion enzymes are structurally conserved These residues are also conserved in evolution Mutagenesis suggests these residues may exert an effect on DNA- and RNA processing Our work offers insights into CRISPR/Cas9, spliceosome, and DNA/RNA polymerases
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36
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Bao P, Höbartner C, Hartmuth K, Lührmann R. Yeast Prp2 liberates the 5' splice site and the branch site adenosine for catalysis of pre-mRNA splicing. RNA (NEW YORK, N.Y.) 2017; 23:1770-1779. [PMID: 28864812 PMCID: PMC5688998 DOI: 10.1261/rna.063115.117] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/24/2017] [Accepted: 08/31/2017] [Indexed: 05/20/2023]
Abstract
The RNA helicase Prp2 facilitates the remodeling of the spliceosomal Bact complex to the catalytically activated B* complex just before step one of splicing. As a high-resolution cryo-EM structure of the B* complex is currently lacking, the precise spliceosome remodeling events mediated by Prp2 remain poorly understood. To investigate the latter, we used chemical structure probing to compare the RNA structure of purified yeast Bact and B* complexes. Our studies reveal deviations from conventional RNA helices in the functionally important U6 snRNA internal stem-loop and U2/U6 helix Ib in the activated Bact complex, and to a lesser extent in B*. Interestingly, the N7 of U6-G60 of the catalytic triad becomes accessible to DMS modification in the B* complex, suggesting that the Hoogsteen interaction with U6-A52 is destabilized in B*. Our data show that Prp2 action does not unwind double-stranded RNA, but enhances the flexibility of the first step reactants, the pre-mRNA's 5' splice site and branch site adenosine. Prp2 therefore appears to act primarily as an RNPase to achieve catalytic activation by liberating the first step reactants in preparation for catalysis of the first step of splicing.
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Affiliation(s)
- Penghui Bao
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
| | - Claudia Höbartner
- Research Group Nucleic Acid Chemistry, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
- Institute for Organic and Biomolecular Chemistry, Georg-August-University, 37077 Göttingen, Germany
| | - Klaus Hartmuth
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
| | - Reinhard Lührmann
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
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37
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Bai R, Yan C, Wan R, Lei J, Shi Y. Structure of the Post-catalytic Spliceosome from Saccharomyces cerevisiae. Cell 2017; 171:1589-1598.e8. [PMID: 29153833 DOI: 10.1016/j.cell.2017.10.038] [Citation(s) in RCA: 65] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2017] [Revised: 10/12/2017] [Accepted: 10/23/2017] [Indexed: 01/02/2023]
Abstract
Removal of an intron from a pre-mRNA by the spliceosome results in the ligation of two exons in the post-catalytic spliceosome (known as the P complex). Here, we present a cryo-EM structure of the P complex from Saccharomyces cerevisiae at an average resolution of 3.6 Å. The ligated exon is held in the active site through RNA-RNA contacts. Three bases at the 3' end of the 5' exon remain anchored to loop I of U5 small nuclear RNA, and the conserved AG nucleotides of the 3'-splice site (3'SS) are specifically recognized by the invariant adenine of the branch point sequence, the guanine base at the 5' end of the 5'SS, and an adenine base of U6 snRNA. The 3'SS is stabilized through an interaction with the 1585-loop of Prp8. The P complex structure provides a view on splice junction formation critical for understanding the complete splicing cycle.
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Affiliation(s)
- Rui Bai
- Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences and School of Medicine, Tsinghua University, Beijing 100084, China
| | - Chuangye Yan
- Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences and School of Medicine, Tsinghua University, Beijing 100084, China
| | - Ruixue Wan
- Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences and School of Medicine, Tsinghua University, Beijing 100084, China
| | - Jianlin Lei
- Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences and School of Medicine, Tsinghua University, Beijing 100084, China; Technology Center for Protein Sciences, Ministry of Education Key Laboratory of Protein Sciences, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Yigong Shi
- Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences and School of Medicine, Tsinghua University, Beijing 100084, China; Institute of Biology, Westlake Institute for Advanced Study, Westlake University, Shilongshan Road No. 18, Xihu District, Hangzhou 310064, Zhejiang Province, China.
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38
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Wilkinson ME, Fica SM, Galej WP, Norman CM, Newman AJ, Nagai K. Postcatalytic spliceosome structure reveals mechanism of 3'-splice site selection. Science 2017; 358:1283-1288. [PMID: 29146871 DOI: 10.1126/science.aar3729] [Citation(s) in RCA: 78] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2017] [Accepted: 11/09/2017] [Indexed: 12/27/2022]
Abstract
Introns are removed from eukaryotic messenger RNA precursors by the spliceosome in two transesterification reactions-branching and exon ligation. The mechanism of 3'-splice site recognition during exon ligation has remained unclear. Here we present the 3.7-angstrom cryo-electron microscopy structure of the yeast P-complex spliceosome immediately after exon ligation. The 3'-splice site AG dinucleotide is recognized through non-Watson-Crick pairing with the 5' splice site and the branch-point adenosine. After the branching reaction, protein factors work together to remodel the spliceosome and stabilize a conformation competent for 3'-splice site docking, thereby promoting exon ligation. The structure accounts for the strict conservation of the GU and AG dinucleotides at the 5' and 3' ends of introns and provides insight into the catalytic mechanism of exon ligation.
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Affiliation(s)
- Max E Wilkinson
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK.
| | - Sebastian M Fica
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
| | | | | | | | - Kiyoshi Nagai
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK.
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39
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snRNP proteins in health and disease. Semin Cell Dev Biol 2017; 79:92-102. [PMID: 29037818 DOI: 10.1016/j.semcdb.2017.10.011] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2017] [Revised: 10/09/2017] [Accepted: 10/12/2017] [Indexed: 01/16/2023]
Abstract
Split gene architecture of most human genes requires removal of intervening sequences by mRNA splicing that occurs on large multiprotein complexes called spliceosomes. Mutations compromising several spliceosomal components have been recorded in degenerative syndromes and haematological neoplasia, thereby highlighting the importance of accurate splicing execution in homeostasis of assorted adult tissues. Moreover, insufficient splicing underlies defective development of craniofacial skeleton and upper extremities. This review summarizes recent advances in the understanding of splicing factor function deduced from cryo-EM structures. We combine these data with the characterization of splicing factors implicated in hereditary or somatic disorders, with a focus on potential functional consequences the mutations may elicit in spliceosome assembly and/or performance. Given aberrant splicing or perturbations in splicing efficiency substantially underpin disease pathogenesis, profound understanding of the mis-splicing principles may open new therapeutic vistas. In three major sections dedicated to retinal dystrophies, hereditary acrofacial syndromes, and haematological malignancies, we delineate the noticeable variety of conditions associated with dysfunctional splicing and accentuate recurrent patterns in splicing defects.
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40
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Fica SM, Nagai K. Cryo-electron microscopy snapshots of the spliceosome: structural insights into a dynamic ribonucleoprotein machine. Nat Struct Mol Biol 2017; 24:791-799. [PMID: 28981077 DOI: 10.1038/nsmb.3463] [Citation(s) in RCA: 129] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2017] [Accepted: 08/10/2017] [Indexed: 12/18/2022]
Abstract
The spliceosome excises introns from pre-messenger RNAs using an RNA-based active site that is cradled by a dynamic protein scaffold. A recent revolution in cryo-electron microscopy (cryo-EM) has led to near-atomic-resolution structures of key spliceosome complexes that provide insight into the mechanism of activation, splice site positioning, catalysis, protein rearrangements and ATPase-mediated dynamics of the active site. The cryo-EM structures rationalize decades of observations from genetic and biochemical studies and provide a molecular framework for future functional studies.
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41
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Mechanistic insights into precursor messenger RNA splicing by the spliceosome. Nat Rev Mol Cell Biol 2017; 18:655-670. [DOI: 10.1038/nrm.2017.86] [Citation(s) in RCA: 234] [Impact Index Per Article: 33.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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42
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Scheres SH, Nagai K. CryoEM structures of spliceosomal complexes reveal the molecular mechanism of pre-mRNA splicing. Curr Opin Struct Biol 2017; 46:130-139. [PMID: 28888105 DOI: 10.1016/j.sbi.2017.08.001] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2017] [Revised: 07/26/2017] [Accepted: 08/07/2017] [Indexed: 01/09/2023]
Abstract
The spliceosome is an intricate molecular machine which catalyses the removal of introns from eukaryotic mRNA precursors by two trans-esterification reactions (branching and exon ligation) to produce mature mRNA with uninterrupted protein coding sequences. The structures of the spliceosome in several key states determined by electron cryo-microscopy have greatly advanced our understanding of its molecular mechanism. The catalytic RNA core is formed during the activation of the fully assembled B to Bact complex and remains largely unchanged throughout the splicing cycle. RNA helicases and step specific factors regulate docking and undocking of the substrates (branch site and 3' splice site) to the single RNA-based active site to catalyse the two trans-esterification reactions.
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Affiliation(s)
- Sjors Hw Scheres
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, United Kingdom.
| | - Kiyoshi Nagai
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, United Kingdom.
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43
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Abstract
Group II introns are large, autocatalytic ribozymes that catalyze RNA splicing and retrotransposition. Splicing by group II introns plays a major role in the metabolism of plants, fungi, and yeast and contributes to genetic variation in many bacteria. Group II introns have played a major role in genome evolution, as they are likely progenitors of spliceosomal introns, retroelements, and other machinery that controls genetic variation and stability. The structure and catalytic mechanism of group II introns have recently been elucidated through a combination of genetics, chemical biology, solution biochemistry, and crystallography. These studies reveal a dynamic machine that cycles progressively through multiple conformations as it stimulates the various stages of splicing. A central active site, containing a reactive metal ion cluster, catalyzes both steps of self-splicing. These studies provide insights into RNA structure, folding, and catalysis, as they raise new questions about the behavior of RNA machines.
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Affiliation(s)
- Anna Marie Pyle
- Department of Molecular, Cellular and Developmental Biology, Yale University, Howard Hughes Medical Institute, New Haven, Connecticut 06520.,Department of Chemistry, Yale University, Howard Hughes Medical Institute, New Haven, Connecticut 06520;
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44
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Costa M, Walbott H, Monachello D, Westhof E, Michel F. Crystal structures of a group II intron lariat primed for reverse splicing. Science 2017; 354:354/6316/aaf9258. [PMID: 27934709 DOI: 10.1126/science.aaf9258] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2016] [Accepted: 10/27/2016] [Indexed: 12/28/2022]
Abstract
The 2'-5' branch of nuclear premessenger introns is believed to have been inherited from self-splicing group II introns, which are retrotransposons of bacterial origin. Our crystal structures at 3.4 and 3.5 angstrom of an excised group II intron in branched ("lariat") form show that the 2'-5' branch organizes a network of active-site tertiary interactions that position the intron terminal 3'-hydroxyl group into a configuration poised to initiate reverse splicing, the first step in retrotransposition. Moreover, the branchpoint and flanking helices must undergo a base-pairing switch after branch formation. A group II-based model of the active site of the nuclear splicing machinery (the spliceosome) is proposed. The crucial role of the lariat conformation in active-site assembly and catalysis explains its prevalence in modern splicing.
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Affiliation(s)
- Maria Costa
- Group II introns as ribozymes and retrotransposons, Institute for Integrative Biology of the Cell (I2BC), UMR 9198 CNRS, Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA), University Paris-Sud, University Paris-Saclay, 1 Avenue de la Terrasse, Bâtiment 26, 91198 Gif-sur-Yvette cedex, France.
| | - Hélène Walbott
- Structure and Dynamics of RNA, I2BC, UMR 9198 CNRS, CEA, University Paris-Sud, University Paris-Saclay, 91198 Gif-sur-Yvette cedex, France
| | - Dario Monachello
- Group II introns as ribozymes and retrotransposons, Institute for Integrative Biology of the Cell (I2BC), UMR 9198 CNRS, Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA), University Paris-Sud, University Paris-Saclay, 1 Avenue de la Terrasse, Bâtiment 26, 91198 Gif-sur-Yvette cedex, France
| | - Eric Westhof
- Architecture and Reactivity of RNA, Institute of Molecular and Cellular Biology of the CNRS, University of Strasbourg, 15 rue René Descartes, 67084 Strasbourg, France
| | - François Michel
- Group II introns as ribozymes and retrotransposons, Institute for Integrative Biology of the Cell (I2BC), UMR 9198 CNRS, Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA), University Paris-Sud, University Paris-Saclay, 1 Avenue de la Terrasse, Bâtiment 26, 91198 Gif-sur-Yvette cedex, France
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45
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Shi Y. The Spliceosome: A Protein-Directed Metalloribozyme. J Mol Biol 2017; 429:2640-2653. [PMID: 28733144 DOI: 10.1016/j.jmb.2017.07.010] [Citation(s) in RCA: 69] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2017] [Revised: 07/13/2017] [Accepted: 07/14/2017] [Indexed: 11/15/2022]
Abstract
Pre-mRNA splicing is executed by the ribonucleoprotein machinery spliceosome. Nearly 40 years after the discovery of pre-mRNA splicing, the atomic structure of the spliceosome has finally come to light. Four distinct conformational states of the yeast spliceosome have been captured at atomic or near-atomic resolutions. Two catalytic metal ions at the active site are specifically coordinated by the U6 small nuclear RNA (snRNA) and catalyze both the branching reaction and the exon ligation. Of the three snRNAs in the fully assembled spliceosome, U5 and U6, along with 30 contiguous nucleotides of U2 at its 5'-end, remain structurally rigid throughout the splicing reaction. The rigidity of these RNA elements is safeguarded by Prp8 and 16 core protein components, which maintain the same overall conformation in all structurally characterized spliceosomes during the splicing reaction. Only the sequences downstream of nucleotide 30 of U2 snRNA are mobile; their movement, directed by the protein components, delivers the intron branch site into the close proximity of the 5'-splice site for the branching reaction. A set of additional structural rearrangement is required for exon ligation, and the lariat junction is moved out of the active site for recruitment of the 3'-splice site and 3'-exon. The spliceosome is proven to be a protein-directed metalloribozyme.
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Affiliation(s)
- Yigong Shi
- Beijing Advanced Innovation Center for Structural Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China; Institute of Biology, Westlake Institute for Advanced Study, 18 Shilongshan Road, Xihu District, Hangzhou 310064, Zhejiang Province, Province, China.
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46
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Plaschka C, Lin PC, Nagai K. Structure of a pre-catalytic spliceosome. Nature 2017; 546:617-621. [PMID: 28530653 PMCID: PMC5503131 DOI: 10.1038/nature22799] [Citation(s) in RCA: 160] [Impact Index Per Article: 22.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2017] [Accepted: 05/02/2017] [Indexed: 12/12/2022]
Abstract
Intron removal requires assembly of the spliceosome on precursor mRNA (pre-mRNA) and extensive remodelling to form the spliceosome's catalytic centre. Here we report the cryo-electron microscopy structure of the yeast Saccharomyces cerevisiae pre-catalytic B complex spliceosome at near-atomic resolution. The mobile U2 small nuclear ribonucleoprotein particle (snRNP) associates with U4/U6.U5 tri-snRNP through the U2/U6 helix II and an interface between U4/U6 di-snRNP and the U2 snRNP SF3b-containing domain, which also transiently contacts the helicase Brr2. The 3' region of the U2 snRNP is flexibly attached to the SF3b-containing domain and protrudes over the concave surface of tri-snRNP, where the U1 snRNP may reside before its release from the pre-mRNA 5' splice site. The U6 ACAGAGA sequence forms a hairpin that weakly tethers the 5' splice site. The B complex proteins Prp38, Snu23 and Spp381 bind the Prp8 N-terminal domain and stabilize U6 ACAGAGA stem-pre-mRNA and Brr2-U4 small nuclear RNA interactions. These results provide important insights into the events leading to active site formation.
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MESH Headings
- Base Sequence
- Biocatalysis
- Catalytic Domain
- Cryoelectron Microscopy
- Introns/genetics
- Models, Biological
- Models, Molecular
- Nuclear Proteins/chemistry
- Nuclear Proteins/metabolism
- Protein Binding
- Protein Domains
- Protein Stability
- RNA Helicases/chemistry
- RNA Helicases/metabolism
- RNA Helicases/ultrastructure
- RNA Precursors/genetics
- RNA Precursors/metabolism
- RNA Precursors/ultrastructure
- RNA Splice Sites/genetics
- RNA Splicing
- RNA Splicing Factors/chemistry
- RNA Splicing Factors/metabolism
- RNA, Small Nuclear/chemistry
- RNA, Small Nuclear/metabolism
- Ribonucleoprotein, U2 Small Nuclear/chemistry
- Ribonucleoprotein, U2 Small Nuclear/metabolism
- Ribonucleoprotein, U4-U6 Small Nuclear/chemistry
- Ribonucleoprotein, U4-U6 Small Nuclear/metabolism
- Ribonucleoprotein, U5 Small Nuclear/chemistry
- Ribonucleoprotein, U5 Small Nuclear/metabolism
- Ribonucleoproteins, Small Nuclear/chemistry
- Ribonucleoproteins, Small Nuclear/metabolism
- Saccharomyces cerevisiae/chemistry
- Saccharomyces cerevisiae/genetics
- Saccharomyces cerevisiae Proteins/chemistry
- Saccharomyces cerevisiae Proteins/metabolism
- Saccharomyces cerevisiae Proteins/ultrastructure
- Spliceosomes/chemistry
- Spliceosomes/metabolism
- Spliceosomes/ultrastructure
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Affiliation(s)
- Clemens Plaschka
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, United Kingdom
| | - Pei-Chun Lin
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, United Kingdom
| | - Kiyoshi Nagai
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, United Kingdom
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47
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Zhao C, Pyle AM. Structural Insights into the Mechanism of Group II Intron Splicing. Trends Biochem Sci 2017; 42:470-482. [PMID: 28438387 PMCID: PMC5492998 DOI: 10.1016/j.tibs.2017.03.007] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2017] [Revised: 03/28/2017] [Accepted: 03/30/2017] [Indexed: 12/19/2022]
Abstract
While the major architectural features and active-site components of group II introns have been known for almost a decade, information on the individual stages of splicing has been lacking. Recent advances in crystallography and cryo-electron microscopy (cryo-EM) have provided major new insights into the structure of intact lariat introns. Conformational changes that mediate the steps of splicing and retrotransposition are being elucidated, revealing the dynamic, highly coordinated motions that are required for group II intron activity. Finally, these ribozymes can now be viewed in their larger, more natural context as components of holoenzymes that include encoded maturase proteins. These studies expand our understanding of group II intron structural diversity and evolution, while setting the stage for rigorous mechanistic analysis of RNA splicing machines.
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Affiliation(s)
- Chen Zhao
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
| | - Anna Marie Pyle
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, CT 06520, USA; Department of Chemistry, Yale University, New Haven, CT 06520, USA; Howard Hughes Medical Institute, Chevy Chase, MD 20815, USA.
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48
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Mechanistic Insights Into Catalytic RNA-Protein Complexes Involved in Translation of the Genetic Code. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2017. [PMID: 28683922 DOI: 10.1016/bs.apcsb.2017.04.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/28/2023]
Abstract
The contemporary world is an "RNA-protein world" rather than a "protein world" and tracing its evolutionary origins is of great interest and importance. The different RNAs that function in close collaboration with proteins are involved in several key physiological processes, including catalysis. Ribosome-the complex megadalton cellular machinery that translates genetic information encoded in nucleotide sequence to amino acid sequence-epitomizes such an association between RNA and protein. RNAs that can catalyze biochemical reactions are known as ribozymes. They usually employ general acid-base catalytic mechanism, often involving the 2'-OH of RNA that activates and/or stabilizes a nucleophile during the reaction pathway. The protein component of such RNA-protein complexes (RNPCs) mostly serves as a scaffold which provides an environment conducive for the RNA to function, or as a mediator for other interacting partners. In this review, we describe those RNPCs that are involved at different stages of protein biosynthesis and in which RNA performs the catalytic function; the focus of the account is on highlighting mechanistic aspects of these complexes. We also provide a perspective on such associations in the context of proofreading during translation of the genetic code. The latter aspect is not much appreciated and recent works suggest that this is an avenue worth exploring, since an understanding of the subject can provide useful insights into how RNAs collaborate with proteins to ensure fidelity during these essential cellular processes. It may also aid in comprehending evolutionary aspects of such associations.
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49
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Zhao C, Pyle AM. The group II intron maturase: a reverse transcriptase and splicing factor go hand in hand. Curr Opin Struct Biol 2017; 47:30-39. [PMID: 28528306 DOI: 10.1016/j.sbi.2017.05.002] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2016] [Accepted: 05/02/2017] [Indexed: 12/28/2022]
Abstract
The splicing of group II introns in vivo requires the assistance of a multifunctional intron encoded protein (IEP, or maturase). Each IEP is also a reverse-transcriptase enzyme that enables group II introns to behave as mobile genetic elements. During splicing or retro-transposition, each group II intron forms a tight, specific complex with its own encoded IEP, resulting in a highly reactive holoenzyme. This review focuses on the structural basis for IEP function, as revealed by recent crystal structures of an IEP reverse transcriptase domain and cryo-EM structures of an IEP-intron complex. These structures explain how the same IEP scaffold is utilized for intron recognition, splicing and reverse transcription, while providing a physical basis for understanding the evolutionary transformation of the IEP into the eukaryotic splicing factor Prp8.
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Affiliation(s)
- Chen Zhao
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
| | - Anna Marie Pyle
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, CT 06520, USA; Department of Chemistry, Yale University, New Haven, CT 06520, USA; Howard Hughes Medical Institute, Chevy Chase, MD 20815, USA.
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50
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Sidarovich A, Will CL, Anokhina MM, Ceballos J, Sievers S, Agafonov DE, Samatov T, Bao P, Kastner B, Urlaub H, Waldmann H, Lührmann R. Identification of a small molecule inhibitor that stalls splicing at an early step of spliceosome activation. eLife 2017; 6. [PMID: 28300534 PMCID: PMC5354520 DOI: 10.7554/elife.23533] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2016] [Accepted: 02/26/2017] [Indexed: 11/13/2022] Open
Abstract
Small molecule inhibitors of pre-mRNA splicing are important tools for identifying new spliceosome assembly intermediates, allowing a finer dissection of spliceosome dynamics and function. Here, we identified a small molecule that inhibits human pre-mRNA splicing at an intermediate stage during conversion of pre-catalytic spliceosomal B complexes into activated Bact complexes. Characterization of the stalled complexes (designated B028) revealed that U4/U6 snRNP proteins are released during activation before the U6 Lsm and B-specific proteins, and before recruitment and/or stable incorporation of Prp19/CDC5L complex and other Bact complex proteins. The U2/U6 RNA network in B028 complexes differs from that of the Bact complex, consistent with the idea that the catalytic RNA core forms stepwise during the B to Bact transition and is likely stabilized by the Prp19/CDC5L complex and related proteins. Taken together, our data provide new insights into the RNP rearrangements and extensive exchange of proteins that occurs during spliceosome activation. DOI:http://dx.doi.org/10.7554/eLife.23533.001
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Affiliation(s)
- Anzhalika Sidarovich
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Cindy L Will
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Maria M Anokhina
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Javier Ceballos
- Department of Chemical Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | - Sonja Sievers
- Compound Management and Screening Center, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | - Dmitry E Agafonov
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Timur Samatov
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Penghui Bao
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Berthold Kastner
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Henning Urlaub
- Bioanalytics Group, Institute for Clinical Chemistry Göttingen, University Medical Center, Göttingen, Germany
| | - Herbert Waldmann
- Department of Chemical Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | - Reinhard Lührmann
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
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