1
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Liu N, Wang HW. Better Cryo-EM Specimen Preparation: How to Deal with the Air-Water Interface? J Mol Biol 2022; 435:167926. [PMID: 36563741 DOI: 10.1016/j.jmb.2022.167926] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2022] [Revised: 12/08/2022] [Accepted: 12/14/2022] [Indexed: 12/24/2022]
Abstract
Cryogenic electron microscopy (cryo-EM) is now one of the most powerful and widely used methods to determine high-resolution structures of macromolecules. A major bottleneck of cryo-EM is to prepare high-quality vitrified specimen, which still faces many practical challenges. During the conventional vitrification process, macromolecules tend to adsorb at the air-water interface (AWI), which is known unfriendly to biological samples. In this review, we outline the nature of AWI and the problems caused by it, such as unpredictable or uneven particle distribution, protein denaturation, dissociation of complex and preferential orientation. We review and discuss the approaches and underlying mechanisms to deal with AWI: 1) Additives, exemplified by detergents, forming a protective layer at AWI and thus preserving the native folds of target macromolecules. 2) Fast vitrification devices based on the idea to freeze in-solution macromolecules before their touching of AWI. 3) Thin layer of continuous supporting films to adsorb macromolecules, and when functionalized with affinity ligands, to specifically anchor the target particles away from the AWI. Among these supporting films, graphene, together with its derivatives, with negligible background noise and mechanical robustness, has emerged as a new generation of support. These strategies have been proven successful in various cases and enable us a better handling of the problems caused by the AWI in cryo-EM specimen preparation.
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Affiliation(s)
- Nan Liu
- Ministry of Education Key Laboratory of Protein Sciences, Beijing Advanced Innovation Center for Structural Biology, Beijing Frontier Research Center for Biological Structures, School of Life Sciences, Tsinghua University, Beijing 100084, China
| | - Hong-Wei Wang
- Ministry of Education Key Laboratory of Protein Sciences, Beijing Advanced Innovation Center for Structural Biology, Beijing Frontier Research Center for Biological Structures, School of Life Sciences, Tsinghua University, Beijing 100084, China; Tsinghua-Peking Joint Center for Life Sciences, Tsinghua University, Beijing 100084, China.
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2
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Shefer K, Boulos A, Gotea V, Arafat M, Ben Chaim Y, Muharram A, Isaac S, Eden A, Sperling J, Elnitski L, Sperling R. A novel role for nucleolin in splice site selection. RNA Biol 2021; 19:333-352. [PMID: 35220879 PMCID: PMC8890436 DOI: 10.1080/15476286.2021.2020455] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2021] [Accepted: 12/10/2021] [Indexed: 01/12/2023] Open
Abstract
Latent 5' splice sites, not normally used, are highly abundant in human introns, but are activated under stress and in cancer, generating thousands of nonsense mRNAs. A previously proposed mechanism to suppress latent splicing was shown to be independent of NMD, with a pivotal role for initiator-tRNA independent of protein translation. To further elucidate this mechanism, we searched for nuclear proteins directly bound to initiator-tRNA. Starting with UV-crosslinking, we identified nucleolin (NCL) interacting directly and specifically with initiator-tRNA in the nucleus, but not in the cytoplasm. Next, we show the association of ini-tRNA and NCL with pre-mRNA. We further show that recovery of suppression of latent splicing by initiator-tRNA complementation is NCL dependent. Finally, upon nucleolin knockdown we show activation of latent splicing in hundreds of coding transcripts having important cellular functions. We thus propose nucleolin, a component of the endogenous spliceosome, through its direct binding to initiator-tRNA and its effect on latent splicing, as the first protein of a nuclear quality control mechanism regulating splice site selection to protect cells from latent splicing that can generate defective mRNAs.
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Affiliation(s)
- Kinneret Shefer
- Department of Genetics, The Hebrew University of Jerusalem, JerusalemIsrael
| | - Ayub Boulos
- Department of Genetics, The Hebrew University of Jerusalem, JerusalemIsrael
| | - Valer Gotea
- Translational and Functional Genomics Branch, National Human Genome Research Institute, NIH, Bethesda, MDUSA
| | - Maram Arafat
- Department of Genetics, The Hebrew University of Jerusalem, JerusalemIsrael
| | - Yair Ben Chaim
- Department of Natural Sciences, The Open University, RaananaIsrael
| | - Aya Muharram
- Department of Genetics, The Hebrew University of Jerusalem, JerusalemIsrael
| | - Sara Isaac
- Department of Cell and Developmental Biology, The Hebrew University of Jerusalem, JerusalemIsrael
| | - Amir Eden
- Department of Cell and Developmental Biology, The Hebrew University of Jerusalem, JerusalemIsrael
| | - Joseph Sperling
- Department of Organic Chemistry, The Weizmann Institute of Science, RehovotIsrael
| | - Laura Elnitski
- Translational and Functional Genomics Branch, National Human Genome Research Institute, NIH, Bethesda, MDUSA
| | - Ruth Sperling
- Department of Genetics, The Hebrew University of Jerusalem, JerusalemIsrael
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3
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Sebbag-Sznajder N, Brody Y, Hochberg-Laufer H, Shav-Tal Y, Sperling J, Sperling R. Dynamic Supraspliceosomes Are Assembled on Different Transcripts Regardless of Their Intron Number and Splicing State. Front Genet 2020; 11:409. [PMID: 32499811 PMCID: PMC7243799 DOI: 10.3389/fgene.2020.00409] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2019] [Accepted: 03/31/2020] [Indexed: 11/13/2022] Open
Abstract
Splicing and alternative splicing of pre-mRNA are key sources in the formation of diversity in the human proteome. These processes have a central role in the regulation of the gene expression pathway. Yet, how spliceosomes are assembled on a multi-intronic pre-mRNA is at present not well understood. To study the spliceosomes assembled in vivo on transcripts with variable number of introns, we examined a series of three related transcripts derived from the β-globin gene, where two transcript types contained increasing number of introns, while one had only an exon. Each transcript had multiple MS2 sequence repeats that can be bound by the MS2 coat protein. Using our protocol for isolation of endogenous spliceosomes under native conditions from cell nuclei, we show that all three transcripts are found in supraspliceosomes – 21 MDa dynamic complexes, sedimenting at 200S in glycerol gradients, and composed of four native spliceosomes connected by the transcript. Affinity purification of complexes assembled on the transcript with most introns (termed E6), using the MS2 tag, confirmed the assembly of E6 in supraspliceosomes with components such as Sm proteins and PSF. Furthermore, splicing inhibition by spliceostatin A did not inhibit the assembly of supraspliceosomes on the E6 transcript, yet increased the percentage of E6 pre-mRNA supraspliceosomes. These findings were corroborated in intact cells, using RNA FISH to detect the MS2-tagged E6 mRNA, together with GFP-tagged splicing factors, showing the assembly of splicing factors SRSF2, U1-70K, and PRP8 onto the E6 transcripts under normal conditions and also when splicing was inhibited. This study shows that different transcripts with different number of introns, or lacking an intron, are assembled in supraspliceosomes even when splicing is inhibited. This assembly starts at the site of transcription and can continue during the life of the transcript in the nucleoplasm. This study further confirms the dynamic and universal nature of supraspliceosomes that package RNA polymerase II transcribed pre-mRNAs into complexes composed of four native spliceosomes connected by the transcript, independent of their length, number of introns, or splicing state.
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Affiliation(s)
| | - Yehuda Brody
- The Mina and Everard Goodman Faculty of Life Sciences and The Institute of Nanotechnology and Advanced Materials, Bar Ilan University, Ramat Gan, Israel
| | - Hodaya Hochberg-Laufer
- The Mina and Everard Goodman Faculty of Life Sciences and The Institute of Nanotechnology and Advanced Materials, Bar Ilan University, Ramat Gan, Israel
| | - Yaron Shav-Tal
- The Mina and Everard Goodman Faculty of Life Sciences and The Institute of Nanotechnology and Advanced Materials, Bar Ilan University, Ramat Gan, Israel
| | - Joseph Sperling
- Department of Organic Chemistry, The Weizmann Institute of Science, Rehovot, Israel
| | - Ruth Sperling
- Department of Genetics, The Hebrew University of Jerusalem, Jerusalem, Israel
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4
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Sperling R. Small non-coding RNA within the endogenous spliceosome and alternative splicing regulation. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2019; 1862:194406. [PMID: 31323432 DOI: 10.1016/j.bbagrm.2019.07.007] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2019] [Revised: 07/08/2019] [Accepted: 07/09/2019] [Indexed: 10/26/2022]
Abstract
Splicing and alternative splicing (AS), which occur in the endogenous spliceosome, play major roles in regulating gene expression, and defects in them are involved in numerous human diseases including cancer. Although the mechanism of the splicing reaction is well understood, the regulation of AS remains to be elucidated. A group of essential regulatory factors in gene expression are small non-coding RNAs (sncRNA): e.g. microRNA, mainly known for their inhibitory role in translation in the cytoplasm; and small nucleolar RNA, known for their role in methylating non-coding RNA in the nucleolus. Here I highlight a new aspect of sncRNAs found within the endogenous spliceosome. Assembled in non-canonical complexes and through different base pairing than their canonical ones, spliceosomal sncRNAs can potentially target different RNAs. Examples of spliceosomal sncRNAs regulating AS, regulating gene expression, and acting in a quality control of AS are reviewed, suggesting novel functions for spliceosomal sncRNAs. 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)
- Ruth Sperling
- Department of Genetics, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
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Pal S, Ganesan K, Eswaran S. Chemical Crosslinking-Mass Spectrometry (CXL-MS) for Proteomics, Antibody-Drug Conjugates (ADCs) and Cryo-Electron Microscopy (cryo-EM). IUBMB Life 2018; 70:947-960. [DOI: 10.1002/iub.1916] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2018] [Revised: 06/06/2018] [Accepted: 06/27/2018] [Indexed: 01/02/2023]
Affiliation(s)
- Shreya Pal
- Amity University Haryana; Manesar Haryana India
| | | | - Sambasivan Eswaran
- Regional Centre for Biotechnology (Established by DBT, Govt. of India under the auspices of UNESCO); NCR Biotech Science Cluster; Faridabad Haryana India
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6
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Wang H, Han W, Takagi J, Cong Y. Yeast Inner-Subunit PA–NZ-1 Labeling Strategy for Accurate Subunit Identification in a Macromolecular Complex through Cryo-EM Analysis. J Mol Biol 2018; 430:1417-1425. [DOI: 10.1016/j.jmb.2018.03.026] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2017] [Revised: 03/14/2018] [Accepted: 03/25/2018] [Indexed: 12/25/2022]
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7
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Ray S, Widom JR, Walter NG. Life under the Microscope: Single-Molecule Fluorescence Highlights the RNA World. Chem Rev 2018; 118:4120-4155. [PMID: 29363314 PMCID: PMC5918467 DOI: 10.1021/acs.chemrev.7b00519] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The emergence of single-molecule (SM) fluorescence techniques has opened up a vast new toolbox for exploring the molecular basis of life. The ability to monitor individual biomolecules in real time enables complex, dynamic folding pathways to be interrogated without the averaging effect of ensemble measurements. In parallel, modern biology has been revolutionized by our emerging understanding of the many functions of RNA. In this comprehensive review, we survey SM fluorescence approaches and discuss how the application of these tools to RNA and RNA-containing macromolecular complexes in vitro has yielded significant insights into the underlying biology. Topics covered include the three-dimensional folding landscapes of a plethora of isolated RNA molecules, their assembly and interactions in RNA-protein complexes, and the relation of these properties to their biological functions. In all of these examples, the use of SM fluorescence methods has revealed critical information beyond the reach of ensemble averages.
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Affiliation(s)
| | | | - Nils G. Walter
- Department of Chemistry, Single Molecule Analysis Group, University of Michigan, Ann Arbor, MI 48109, USA
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8
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Wilkinson ME, Lin PC, Plaschka C, Nagai K. Cryo-EM Studies of Pre-mRNA Splicing: From Sample Preparation to Model Visualization. Annu Rev Biophys 2018; 47:175-199. [PMID: 29494253 DOI: 10.1146/annurev-biophys-070317-033410] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The removal of noncoding introns from pre-messenger RNA (pre-mRNA) is an essential step in eukaryotic gene expression and is catalyzed by a dynamic multi-megadalton ribonucleoprotein complex called the spliceosome. The spliceosome assembles on pre-mRNA substrates by the stepwise addition of small nuclear ribonucleoprotein particles and numerous protein factors. Extensive remodeling is required to form the RNA-based active site and to mediate the pre-mRNA branching and ligation reactions. In the past two years, cryo-electron microscopy (cryo-EM) structures of spliceosomes captured in different assembly and catalytic states have greatly advanced our understanding of its mechanism. This was made possible by long-standing efforts in the purification of spliceosome intermediates as well as recent developments in cryo-EM imaging and computational methodology. The resulting high-resolution densities allow for de novo model building in core regions of the complexes. In peripheral and less ordered regions, the combination of cross-linking, bioinformatics, biochemical, and genetic data is essential for accurate modeling. Here, we summarize these achievements and highlight the critical steps in obtaining near-atomic resolution structures of the spliceosome.
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Affiliation(s)
- Max E Wilkinson
- MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom; , , ,
| | - Pei-Chun Lin
- MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom; , , ,
| | - Clemens Plaschka
- 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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9
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Galganski L, Urbanek MO, Krzyzosiak WJ. Nuclear speckles: molecular organization, biological function and role in disease. Nucleic Acids Res 2017; 45:10350-10368. [PMID: 28977640 PMCID: PMC5737799 DOI: 10.1093/nar/gkx759] [Citation(s) in RCA: 285] [Impact Index Per Article: 40.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2017] [Accepted: 08/18/2017] [Indexed: 12/13/2022] Open
Abstract
The nucleoplasm is not homogenous; it consists of many types of nuclear bodies, also known as nuclear domains or nuclear subcompartments. These self-organizing structures gather machinery involved in various nuclear activities. Nuclear speckles (NSs) or splicing speckles, also called interchromatin granule clusters, were discovered as sites for splicing factor storage and modification. Further studies on transcription and mRNA maturation and export revealed a more general role for splicing speckles in RNA metabolism. Here, we discuss the functional implications of the localization of numerous proteins crucial for epigenetic regulation, chromatin organization, DNA repair and RNA modification to nuclear speckles. We highlight recent advances suggesting that NSs facilitate integrated regulation of gene expression. In addition, we consider the influence of abundant regulatory and signaling proteins, i.e. protein kinases and proteins involved in protein ubiquitination, phosphoinositide signaling and nucleoskeletal organization, on pre-mRNA synthesis and maturation. While many of these regulatory proteins act within NSs, direct evidence for mRNA metabolism events occurring in NSs is still lacking. NSs contribute to numerous human diseases, including cancers and viral infections. In addition, recent data have demonstrated close relationships between these structures and the development of neurological disorders.
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Affiliation(s)
- Lukasz Galganski
- Department of Molecular Biomedicine, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14, 61-704 Poznan, Poland
| | - Martyna O Urbanek
- Department of Molecular Biomedicine, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14, 61-704 Poznan, Poland
| | - Wlodzimierz J Krzyzosiak
- Department of Molecular Biomedicine, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14, 61-704 Poznan, Poland
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10
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Sperling J, Sperling R. Structural studies of the endogenous spliceosome - The supraspliceosome. Methods 2017; 125:70-83. [PMID: 28412289 PMCID: PMC5546952 DOI: 10.1016/j.ymeth.2017.04.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2016] [Revised: 04/01/2017] [Accepted: 04/10/2017] [Indexed: 12/17/2022] Open
Abstract
Pre-mRNA splicing is executed in mammalian cell nuclei within a huge (21MDa) and highly dynamic molecular machine - the supraspliceosome - that individually package pre-mRNA transcripts of different sizes and number of introns into complexes of a unique structure, indicating their universal nature. Detailed structural analysis of this huge and complex structure requires a stepwise approach using hybrid methods. Structural studies of the supraspliceosome by room temperature electron tomography, cryo-electron tomography, and scanning transmission electron microscope mass measurements revealed that it is composed of four native spliceosomes, each resembling an in vitro assembled spliceosome, which are connected by the pre-mRNA. It also elucidated the arrangement of the native spliceosomes within the intact supraspliceosome. Native spliceosomes and supraspliceosomes contain all five spliceosomal U snRNPs together with other splicing factors, and are active in splicing. The structure of the native spliceosome, at a resolution of 20Å, was determined by cryo-electron microscopy, and a unique spatial arrangement of the spliceosomal U snRNPs within the native spliceosome emerged from in silico studies. The supraspliceosome also harbor components for all pre-mRNA processing activities. Thus the supraspliceosome - the endogenous spliceosome - is a stand-alone complete macromolecular machine capable of performing splicing, alternative splicing, and encompass all nuclear pre-mRNA processing activities that the pre-mRNA has to undergo before it can exit from the nucleus to the cytoplasm to encode for protein. Further high-resolution cryo-electron microscopy studies of the endogenous spliceosome are required to decipher the regulation of alternative splicing, and elucidate the network of processing activities within it.
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Affiliation(s)
- Joseph Sperling
- Department of Organic Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Ruth Sperling
- Department of Genetics, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
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11
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Yu G, Li K, Huang P, Jiang X, Jiang W. Antibody-Based Affinity Cryoelectron Microscopy at 2.6-Å Resolution. Structure 2017; 24:1984-1990. [PMID: 27806259 DOI: 10.1016/j.str.2016.09.008] [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: 08/05/2016] [Revised: 09/16/2016] [Accepted: 09/30/2016] [Indexed: 02/02/2023]
Abstract
The affinity cryoelectron microscopy (cryo-EM) approach has been explored in recent years to simplify and/or improve the sample preparation for cryo-EM, which can bring previously challenging specimens such as those of low abundance and/or unpurified ones within reach of the cryo-EM technique. Despite the demonstrated successes for solving structures to low to intermediate resolutions, the lack of near-atomic structures using this approach has led to a common perception of affinity cryo-EM as a niche technique incapable of reaching high resolutions. Here, we report a ∼2.6-Å structure solved using the antibody-based affinity grid approach with low-concentration Tulane virus purified from a low-yield cell-culture system that has been challenging to standard cryo-EM grid preparation. Quantitative analyses of the structure indicate data and reconstruction quality comparable with the conventional grid preparation method using samples at high concentration.
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Affiliation(s)
- Guimei Yu
- Department of Biological Science, Markey Center for Structural Biology, Purdue University, West Lafayette, IN 47907, USA
| | - Kunpeng Li
- Department of Biological Science, Markey Center for Structural Biology, Purdue University, West Lafayette, IN 47907, USA
| | - Pengwei Huang
- Divisions of Infectious Diseases, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229, USA; Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH 45267, USA
| | - Xi Jiang
- Divisions of Infectious Diseases, Cincinnati Children's Hospital Medical Center, Cincinnati, OH 45229, USA; Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH 45267, USA
| | - Wen Jiang
- Department of Biological Science, Markey Center for Structural Biology, Purdue University, West Lafayette, IN 47907, USA.
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12
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Human DBR1 modulates the recycling of snRNPs to affect alternative RNA splicing and contributes to the suppression of cancer development. Oncogene 2017; 36:5382-5391. [PMID: 28504715 PMCID: PMC5608638 DOI: 10.1038/onc.2017.150] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2017] [Revised: 04/03/2017] [Accepted: 04/14/2017] [Indexed: 12/16/2022]
Abstract
The contribution of RNA processing to tumorigenesis is understudied. Here, we report that the human RNA debranching enzyme (hDBR1), when inappropriately regulated, induces oncogenesis by causing RNA processing defects, for example, splicing defects. We found that wild-type p53 and hypoxia-inducible factor 1 co-regulate hDBR1 expression, and insufficient hDBR1 leads to a higher rate of exon skipping. Transcriptomic sequencing confirmed the effect of hDBR1 on RNA splicing, and metabolite profiling supported the observation that neoplasm is triggered by a decrease in hDBR1 expression both in vitro and in vivo. Most importantly, when modulating the expression of hDBR1, which was found to be generally low in malignant human tissues, higher expression of hDBR1 only affected exon-skipping activity in malignant cells. Together, our findings demonstrate previously unrecognized regulation and functions of hDBR1, with immediate clinical implications regarding the regulation of hDBR1 as an effective strategy for combating human cancer.
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13
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Rakesh R, Joseph AP, Bhaskara RM, Srinivasan N. Structural and mechanistic insights into human splicing factor SF3b complex derived using an integrated approach guided by the cryo-EM density maps. RNA Biol 2016; 13:1025-1040. [PMID: 27618338 DOI: 10.1080/15476286.2016.1218590] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Pre-mRNA splicing in eukaryotes is performed by the spliceosome, a highly complex macromolecular machine. SF3b is a multi-protein complex which recognizes the branch point adenosine of pre-mRNA as part of a larger U2 snRNP or U11/U12 di-snRNP in the dynamic spliceosome machinery. Although a cryo-EM map is available for human SF3b complex, the structure and relative spatial arrangement of all components in the complex are not yet known. We have recognized folds of domains in various proteins in the assembly and generated comparative models. Using an integrative approach involving structural and other experimental data, guided by the available cryo-EM density map, we deciphered a pseudo-atomic model of the closed form of SF3b which is found to be a "fuzzy complex" with highly flexible components and multiplicity of folds. Further, the model provides structural information for 5 proteins (SF3b10, SF3b155, SF3b145, SF3b130 and SF3b14b) and localization information for 4 proteins (SF3b10, SF3b145, SF3b130 and SF3b14b) in the assembly for the first time. Integration of this model with the available U11/U12 di-snRNP cryo-EM map enabled elucidation of an open form. This now provides new insights on the mechanistic features involved in the transition between closed and open forms pivoted by a hinge region in the SF3b155 protein that also harbors cancer causing mutations. Moreover, the open form guided model of the 5' end of U12 snRNA, which includes the branch point duplex, shows that the architecture of SF3b acts as a scaffold for U12 snRNA: pre-mRNA branch point duplex formation with potential implications for branch point adenosine recognition fidelity.
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Affiliation(s)
- Ramachandran Rakesh
- a Molecular Biophysics Unit, Indian Institute of Science , Bangalore , India
| | - Agnel Praveen Joseph
- b National Center for Biological Sciences, TIFR, GKVK Campus , Bangalore , India
| | - Ramachandra M Bhaskara
- a Molecular Biophysics Unit, Indian Institute of Science , Bangalore , India.,b National Center for Biological Sciences, TIFR, GKVK Campus , Bangalore , India
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14
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Sperling R. The nuts and bolts of the endogenous spliceosome. WILEY INTERDISCIPLINARY REVIEWS-RNA 2016; 8. [PMID: 27465259 DOI: 10.1002/wrna.1377] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/29/2016] [Revised: 06/14/2016] [Accepted: 06/15/2016] [Indexed: 01/09/2023]
Abstract
The complex life of pre-mRNA from transcription to the production of mRNA that can be exported from the nucleus to the cytoplasm to encode for proteins entails intricate coordination and regulation of a network of processing events. Coordination is required between transcription and splicing and between several processing events including 5' and 3' end processing, splicing, alternative splicing and editing that are major contributors to the diversity of the human proteome, and occur within a huge and dynamic macromolecular machine-the endogenous spliceosome. Detailed mechanistic insight of the splicing reaction was gained from studies of the in vitro spliceosome assembled on a single intron. Because most pre-mRNAs are multiintronic that undergo alternative splicing, the in vivo splicing machine requires additional elements to those of the in vitro machine, to account for all these diverse functions. Information about the endogenous spliceosome is emerging from imaging studies in intact and live cells that support the cotranscriptional commitment to splicing model and provide information about splicing kinetics in vivo. Another source comes from studies of the in vivo assembled spliceosome, isolated from cell nuclei under native conditions-the supraspliceosome-that individually package pre-mRNA transcripts of different sizes and number of introns into complexes of a unique structure, indicating their universal nature. Recent years have portrayed new players affecting alternative splicing and novel connections between splicing, transcription and chromatin. The challenge ahead is to elucidate the structure and function of the endogenous spliceosome and decipher the regulation and coordination of its network of processing activities. WIREs RNA 2017, 8:e1377. doi: 10.1002/wrna.1377 For further resources related to this article, please visit the WIREs website.
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Affiliation(s)
- Ruth Sperling
- Department of Genetics, The Hebrew University of Jerusalem, Jerusalem, Israel
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15
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Yan C, Wan R, Bai R, Huang G, Shi Y. Structure of a yeast activated spliceosome at 3.5 Å resolution. Science 2016; 353:904-11. [PMID: 27445306 DOI: 10.1126/science.aag0291] [Citation(s) in RCA: 200] [Impact Index Per Article: 25.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2016] [Accepted: 07/13/2016] [Indexed: 12/18/2022]
Abstract
Pre-messenger RNA (pre-mRNA) splicing is carried out by the spliceosome, which undergoes an intricate assembly and activation process. Here, we report an atomic structure of an activated spliceosome (known as the B(act) complex) from Saccharomyces cerevisiae, determined by cryo-electron microscopy at an average resolution of 3.52 angstroms. The final refined model contains U2 and U5 small nuclear ribonucleoprotein particles (snRNPs), U6 small nuclear RNA (snRNA), nineteen complex (NTC), NTC-related (NTR) protein, and a 71-nucleotide pre-mRNA molecule, which amount to 13,505 amino acids from 38 proteins and a combined molecular mass of about 1.6 megadaltons. The 5' exon is anchored by loop I of U5 snRNA, whereas the 5' splice site (5'SS) and the branch-point sequence (BPS) of the intron are specifically recognized by U6 and U2 snRNA, respectively. Except for coordination of the catalytic metal ions, the RNA elements at the catalytic cavity of Prp8 are mostly primed for catalysis. The catalytic latency is maintained by the SF3b complex, which encircles the BPS, and the splicing factors Cwc24 and Prp11, which shield the 5' exon-5'SS junction. This structure, together with those determined earlier, outlines a molecular framework for the pre-mRNA splicing reaction.
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Affiliation(s)
- Chuangye Yan
- Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences, 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, 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, Tsinghua University, Beijing 100084, China
| | - Gaoxingyu Huang
- Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life 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, Tsinghua University, Beijing 100084, China.
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16
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Wan R, Yan C, Bai R, Huang G, Shi Y. Structure of a yeast catalytic step I spliceosome at 3.4 Å resolution. Science 2016; 353:895-904. [PMID: 27445308 DOI: 10.1126/science.aag2235] [Citation(s) in RCA: 162] [Impact Index Per Article: 20.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2016] [Accepted: 07/14/2016] [Indexed: 12/30/2022]
Abstract
Each cycle of pre-messenger RNA splicing, carried out by the spliceosome, comprises two sequential transesterification reactions, which result in the removal of an intron and the joining of two exons. Here we report an atomic structure of a catalytic step I spliceosome (known as the C complex) from Saccharomyces cerevisiae, as determined by cryo-electron microscopy at an average resolution of 3.4 angstroms. In the structure, the 2'-OH of the invariant adenine nucleotide in the branch point sequence (BPS) is covalently joined to the phosphate at the 5' end of the 5' splice site (5'SS), forming an intron lariat. The freed 5' exon remains anchored to loop I of U5 small nuclear RNA (snRNA), and the 5'SS and BPS of the intron form duplexes with conserved U6 and U2 snRNA sequences, respectively. Specific placement of these RNA elements at the catalytic cavity of Prp8 is stabilized by 15 protein components, including Snu114 and the splicing factors Cwc21, Cwc22, Cwc25, and Yju2. These features, representing the conformation of the spliceosome after the first-step reaction, predict structural changes that are needed for the execution of the second-step transesterification reaction.
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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, 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, 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, Tsinghua University, Beijing 100084, China
| | - Gaoxingyu Huang
- Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life 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, Tsinghua University, Beijing 100084, China.
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17
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Yu G, Li K, Jiang W. Antibody-based affinity cryo-EM grid. Methods 2016; 100:16-24. [PMID: 26804563 DOI: 10.1016/j.ymeth.2016.01.010] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2015] [Revised: 01/19/2016] [Accepted: 01/20/2016] [Indexed: 12/01/2022] Open
Abstract
The Affinity Grid technique combines sample purification and cryo-Electron Microscopy (cryo-EM) grid preparation into a single step. Several types of affinity surfaces, including functionalized lipids monolayers, streptavidin 2D crystals, and covalently functionalized carbon surfaces have been reported. More recently, we presented a new affinity cryo-EM approach, cryo-SPIEM, which applies the traditional Solid Phase Immune Electron Microscopy (SPIEM) technique to cryo-EM. This approach significantly simplifies the preparation of affinity grids and directly works with native macromolecular complexes without need of target modifications. With wide availability of high affinity and high specificity antibodies, the antibody-based affinity grid would enable cryo-EM studies of the native samples directly from cell cultures, targets of low abundance, and unstable or short-lived intermediate states.
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Affiliation(s)
- Guimei Yu
- Markey Center for Structural Biology, Department of Biological Sciences, Purdue University, West Lafayette, IN, USA
| | - Kunpeng Li
- Markey Center for Structural Biology, Department of Biological Sciences, Purdue University, West Lafayette, IN, USA
| | - Wen Jiang
- Markey Center for Structural Biology, Department of Biological Sciences, Purdue University, West Lafayette, IN, USA.
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18
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Shan H, Wang Z, Zhang F, Xiong Y, Yin CC, Sun F. A local-optimization refinement algorithm in single particle analysis for macromolecular complex with multiple rigid modules. Protein Cell 2015; 7:46-62. [PMID: 26678751 PMCID: PMC4707152 DOI: 10.1007/s13238-015-0229-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2015] [Accepted: 10/11/2015] [Indexed: 11/25/2022] Open
Abstract
Single particle analysis, which can be regarded as an average of signals from thousands or even millions of particle projections, is an efficient method to study the three-dimensional structures of biological macromolecules. An intrinsic assumption in single particle analysis is that all the analyzed particles must have identical composition and conformation. Thus specimen heterogeneity in either composition or conformation has raised great challenges for high-resolution analysis. For particles with multiple conformations, inaccurate alignments and orientation parameters will yield an averaged map with diminished resolution and smeared density. Besides extensive classification approaches, here based on the assumption that the macromolecular complex is made up of multiple rigid modules whose relative orientations and positions are in slight fluctuation around equilibriums, we propose a new method called as local optimization refinement to address this conformational heterogeneity for an improved resolution. The key idea is to optimize the orientation and shift parameters of each rigid module and then reconstruct their three-dimensional structures individually. Using simulated data of 80S/70S ribosomes with relative fluctuations between the large (60S/50S) and the small (40S/30S) subunits, we tested this algorithm and found that the resolutions of both subunits are significantly improved. Our method provides a proof-of-principle solution for high-resolution single particle analysis of macromolecular complexes with dynamic conformations.
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Affiliation(s)
- Hong Shan
- Department of Biophysics, College of Basic Medical Sciences, Peking University Health Science Center, Beijing, 100191, China
| | - Zihao Wang
- Key Lab of Intelligent Information Processing and Advanced Computing Research Lab, Institute of Computing Technology, Chinese Academy of Sciences, Beijing, 100190, China.,University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Fa Zhang
- Key Lab of Intelligent Information Processing and Advanced Computing Research Lab, Institute of Computing Technology, Chinese Academy of Sciences, Beijing, 100190, China
| | - Yong Xiong
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, 06511, USA
| | - Chang-Cheng Yin
- Department of Biophysics, College of Basic Medical Sciences, Peking University Health Science Center, Beijing, 100191, China.
| | - Fei Sun
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China. .,University of Chinese Academy of Sciences, Beijing, 100049, China. .,Center for Biological Imaging, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China.
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19
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Yan C, Hang J, Wan R, Huang M, Wong CCL, Shi Y. Structure of a yeast spliceosome at 3.6-angstrom resolution. Science 2015; 349:1182-91. [DOI: 10.1126/science.aac7629] [Citation(s) in RCA: 278] [Impact Index Per Article: 30.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2015] [Accepted: 08/10/2015] [Indexed: 12/20/2022]
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20
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Shefer K, Sperling J, Sperling R. The Supraspliceosome - A Multi-Task Machine for Regulated Pre-mRNA Processing in the Cell Nucleus. Comput Struct Biotechnol J 2014; 11:113-22. [PMID: 25408845 PMCID: PMC4232567 DOI: 10.1016/j.csbj.2014.09.008] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2014] [Revised: 09/16/2014] [Accepted: 09/18/2014] [Indexed: 01/23/2023] Open
Abstract
Pre-mRNA splicing of Pol II transcripts is executed in the mammalian cell nucleus within a huge (21 MDa) and highly dynamic RNP machine — the supraspliceosome. It is composed of four splicing active native spliceosomes, each resembling an in vitro assembled spliceosome, which are connected by the pre-mRNA. Supraspliceosomes harbor protein splicing factors and all the five-spliceosomal U snRNPs. Recent analysis of specific supraspliceosomes at defined splicing stages revealed that they harbor all five spliceosomal U snRNAs at all splicing stages. Supraspliceosomes harbor additional pre-mRNA processing components, such as the 5′-end and 3′-end processing components, and the RNA editing enzymes ADAR1 and ADAR2. The structure of the native spliceosome, at a resolution of 20 Å, was determined by cryo-EM. A unique spatial arrangement of the spliceosomal U snRNPs within the native spliceosome emerged from in-silico studies, localizing the five U snRNPs mostly within its large subunit, and sheltering the active core components deep within the spliceosomal cavity. The supraspliceosome provides a platform for coordinating the numerous processing steps that the pre-mRNA undergoes: 5′ and 3′-end processing activities, RNA editing, constitutive and alternative splicing, and processing of intronic microRNAs. It also harbors a quality control mechanism termed suppression of splicing (SOS) that, under normal growth conditions, suppresses splicing at abundant intronic latent 5′ splice sites in a reading frame-dependent fashion. Notably, changes in these regulatory processing activities are associated with human disease and cancer. These findings emphasize the supraspliceosome as a multi-task master regulator of pre-mRNA processing in the cell nucleus.
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Affiliation(s)
- Kinneret Shefer
- Department of Organic Chemistry, The Weizmann Institute of Science, Rehovot 76100, Israel
| | - Joseph Sperling
- Department of Organic Chemistry, The Weizmann Institute of Science, Rehovot 76100, Israel
| | - Ruth Sperling
- Department of Genetics, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
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21
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Valdés J, Nozaki T, Sato E, Chiba Y, Nakada-Tsukui K, Villegas-Sepúlveda N, Winkler R, Azuara-Liceaga E, Mendoza-Figueroa MS, Watanabe N, Santos HJ, Saito-Nakano Y, Galindo-Rosales JM. Proteomic analysis of Entamoeba histolytica in vivo assembled pre-mRNA splicing complexes. J Proteomics 2014; 111:30-45. [PMID: 25109466 DOI: 10.1016/j.jprot.2014.07.027] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2014] [Revised: 06/27/2014] [Accepted: 07/23/2014] [Indexed: 10/24/2022]
Abstract
UNLABELLED The genome of the human intestinal parasite Entamoeba histolytica contains nearly 3000 introns and bioinformatic predictions indicate that major and minor spliceosomes occur in Entamoeba. However, except for the U2-, U4-, U5- and U6 snRNAs, no other splicing factor has been cloned and characterized. Here, we HA-tagged cloned the snRNP component U1A and assessed its expression and nuclear localization. Because the snRNP-free U1A form interacts with polyadenylate-binding protein, HA-U1A immunoprecipitates could identify early and late splicing complexes. Avoiding Entamoeba's endonucleases and ensuring the precipitation of RNA-binding proteins, parasite cultures were UV cross-linked prior to nuclear fraction immunoprecipitations with HA antibodies, and precipitates were subjected to tandem mass spectrometry (MS/MS) analyses. To discriminate their nuclear roles (chromatin-, co-transcriptional-, splicing-related), MS/MS analyses were carried out with proteins eluted with MS2-GST-sepharose from nuclear extracts of an MS2 aptamer-tagged Rabx13 intron amoeba transformant. Thus, we probed thirty-six Entamoeba proteins corresponding to 32 cognate splicing-specific factors, including 13 DExH/D helicases required for all stages of splicing, and 12 different splicing-related helicases were identified also. Furthermore 50 additional proteins, possibly involved in co-transcriptional processes were identified, revealing the complexity of co-transcriptional splicing in Entamoeba. Some of these later factors were not previously found in splicing complex analyses. BIOLOGICAL SIGNIFICANCE Numerous facts about the splicing of the nearly 3000 introns of the Entamoeba genome have not been unraveled, particularly the splicing factors and their activities. Considering that many of such introns are located in metabolic genes, the knowledge of the splicing cues has the potential to be used to attack or control the parasite. We have found numerous new splicing-related factors which could have therapeutic benefit. We also detected all the DExH/A RNA helicases involved in splicing and splicing proofreading control. Still, Entamoeba is very inefficient in splicing fidelity, thus we may have found a possible model system to study these processes.
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Affiliation(s)
- Jesús Valdés
- Departament of Biochemistry, CINVESTAV, México D.F., Mexico.
| | - Tomoyoshi Nozaki
- Department of Parasitology, National Institute of Infectious Diseases, Tokyo, Japan
| | - Emi Sato
- Department of Parasitology, National Institute of Infectious Diseases, Tokyo, Japan
| | - Yoko Chiba
- University of Tsukuba, Graduate School of Life and Environmental Sciences, Tsukuba, Japan
| | - Kumiko Nakada-Tsukui
- Department of Parasitology, National Institute of Infectious Diseases, Tokyo, Japan
| | | | - Robert Winkler
- Department of Biotechnology and Biochemistry, CINVESTAV Unidad Irapuato, Irapuato, Guanajuato, Mexico
| | | | | | - Natsuki Watanabe
- University of Tsukuba, Graduate School of Life and Environmental Sciences, Tsukuba, Japan
| | - Herbert J Santos
- Department of Parasitology, National Institute of Infectious Diseases, Tokyo, Japan; University of Tsukuba, Graduate School of Life and Environmental Sciences, Tsukuba, Japan; Institute of Biology, College of Science, University of the Philippines Diliman, Quezon City, Philippines
| | - Yumiko Saito-Nakano
- Department of Parasitology, National Institute of Infectious Diseases, Tokyo, Japan
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22
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Noel JK, Whitford PC. How Simulations Reveal Dynamics, Disorder, and the Energy Landscapes of Biomolecular Function. Isr J Chem 2014. [DOI: 10.1002/ijch.201400018] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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23
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Supraspliceosomes at defined functional states portray the pre-assembled nature of the pre-mRNA processing machine in the cell nucleus. Int J Mol Sci 2014; 15:11637-64. [PMID: 24983480 PMCID: PMC4139805 DOI: 10.3390/ijms150711637] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2014] [Revised: 06/05/2014] [Accepted: 06/18/2014] [Indexed: 02/02/2023] Open
Abstract
When isolated from mammalian cell nuclei, all nuclear pre-mRNAs are packaged in multi-subunit large ribonucleoprotein complexes-supraspliceosomes-composed of four native spliceosomes interconnected by the pre-mRNA. Supraspliceosomes contain all five spliceosomal U snRNPs, together with other splicing factors, and are functional in splicing. Supraspliceosomes studied thus far represent the steady-state population of nuclear pre-mRNAs that were isolated at different stages of the splicing reaction. To analyze specific splicing complexes, here, we affinity purified Pseudomonas aeruginosa phage 7 (PP7)-tagged splicing complexes assembled in vivo on Adenovirus Major Late (AdML) transcripts at specific functional stages, and characterized them using molecular techniques including mass spectrometry. First, we show that these affinity purified splicing complexes assembled on PP7-tagged AdML mRNA or on PP7-tagged AdML pre-mRNA are assembled in supraspliceosomes. Second, similar to the general population of supraspliceosomes, these defined supraspliceosomes populations are assembled with all five U snRNPs at all splicing stages. This study shows that dynamic changes in base-pairing interactions of U snRNA:U snRNA and U snRNA:pre-mRNA that occur in vivo during the splicing reaction do not require changes in U snRNP composition of the supraspliceosome. Furthermore, there is no need to reassemble a native spliceosome for the splicing of each intron, and rearrangements of the interactions will suffice.
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24
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Gupta K, Contreras LM, Smith D, Qu G, Huang T, Spruce LA, Seeholzer SH, Belfort M, Van Duyne GD. Quaternary arrangement of an active, native group II intron ribonucleoprotein complex revealed by small-angle X-ray scattering. Nucleic Acids Res 2014; 42:5347-60. [PMID: 24567547 PMCID: PMC4005650 DOI: 10.1093/nar/gku140] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The stable ribonucleoprotein (RNP) complex formed between the Lactococcus lactis group II intron and its self-encoded LtrA protein is essential for the intron's genetic mobility. In this study, we report the biochemical, compositional, hydrodynamic and structural properties of active group II intron RNP particles (+A) isolated from its native host using a novel purification scheme. We employed small-angle X-ray scattering to determine the structural properties of these particles as they exist in solution. Using sucrose as a contrasting agent, we derived a two-phase quaternary model of the protein-RNA complex. This approach revealed that the spatial properties of the complex are largely defined by the RNA component, with the protein dimer located near the center of mass. A transfer RNA fusion engineered into domain II of the intron provided a distinct landmark consistent with this interpretation. Comparison of the derived +A RNP shape with that of the previously reported precursor intron (ΔA) particle extends previous findings that the loosely packed precursor RNP undergoes a dramatic conformational change as it compacts into its active form. Our results provide insights into the quaternary arrangement of these RNP complexes in solution, an important step to understanding the transition of the group II intron from the precursor to a species fully active for DNA invasion.
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Affiliation(s)
- Kushol Gupta
- Department of Biochemistry & Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104-6059, USA, Department of Chemical Engineering, University of Texas at Austin, Austin, TX 78712, USA, Wadsworth Center, NYS Department of Health, Albany, NY 12201, USA, Department of Biological Sciences and RNA Institute, University at Albany, State University of New York, Albany, NY 12222, USA, SUNY Downstate Medical Center, University Hospital, Brooklyn, NY 11203, USA and Children's Hospital of Philadelphia Research Institute, Philadelphia, PA 19104, USA
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25
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Agranat-Tamir L, Shomron N, Sperling J, Sperling R. Interplay between pre-mRNA splicing and microRNA biogenesis within the supraspliceosome. Nucleic Acids Res 2014; 42:4640-51. [PMID: 24464992 PMCID: PMC3985634 DOI: 10.1093/nar/gkt1413] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
MicroRNAs (miRNAs) are central regulators of gene expression, and a large fraction of them are encoded in introns of RNA polymerase II transcripts. Thus, the biogenesis of intronic miRNAs by the microprocessor and the splicing of their host introns by the spliceosome require coordination between these processing events. This cross-talk is addressed here. We show that key microprocessor proteins Drosha and DGCR8 as well as pre-miRNAs cosediment with supraspliceosomes, where nuclear posttranscriptional processing is executed. We further show that inhibition of splicing increases miRNAs expression, whereas knock-down of Drosha increases splicing. We identified a novel splicing event in intron 13 of MCM7, where the miR-106b-25 cluster is located. The unique splice isoform includes a hosted pre-miRNA in the extended exon and excludes its processing. This indicates a possible mechanism of altering the levels of different miRNAs originating from the same transcript. Altogether, our study indicates interplay between the splicing and microprocessor machineries within a supraspliceosome context.
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Affiliation(s)
- Lily Agranat-Tamir
- Department of Genetics, The Hebrew University of Jerusalem, Jerusalem 91904, Israel, Department of Cell and Developmental Biology, Sackler Faculty of Medicine, Tel Aviv University, 69978 Tel Aviv, Israel and Department of Organic Chemistry, The Weizmann Institute of Science, Rehovot 76100, Israel
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26
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Sperling J, Sperling R. 38 A network of interactions within the supraspliceosome. J Biomol Struct Dyn 2013. [DOI: 10.1080/07391102.2013.786471] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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27
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Frankenstein Z, Sperling J, Sperling R, Eisenstein M. A unique spatial arrangement of the snRNPs within the native spliceosome emerges from in silico studies. Structure 2012; 20:1097-106. [PMID: 22578543 DOI: 10.1016/j.str.2012.03.022] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2011] [Revised: 02/25/2012] [Accepted: 03/26/2012] [Indexed: 02/05/2023]
Abstract
The spliceosome is a mega-Dalton ribonucleoprotein (RNP) assembly that processes primary RNA transcripts, producing functional mRNA. The electron microscopy structures of the native spliceosome and of several spliceosomal subcomplexes are available; however, the spatial arrangement of the latter within the native spliceosome is not known. We designed a computational procedure to efficiently fit thousands of conformers into the spliceosome envelope. Despite the low resolution limitations, we obtained only one model that complies with the available biochemical data. Our model localizes the five small nuclear RNPs (snRNPs) mostly within the large subunit of the native spliceosome, requiring only minor conformation changes. The remaining free volume presumably accommodates additional spliceosomal components. The constituents of the active core of the spliceosome are juxtaposed, forming a continuous surface deep within the large spliceosomal cavity, which provides a sheltered environment for the splicing reaction.
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Affiliation(s)
- Ziv Frankenstein
- Department of Structural Biology, Weizmann Institute of Science, Rehovot 76100, Israel
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28
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Andrulis ED. Theory of the origin, evolution, and nature of life. Life (Basel) 2011; 2:1-105. [PMID: 25382118 PMCID: PMC4187144 DOI: 10.3390/life2010001] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2011] [Revised: 12/10/2011] [Accepted: 12/13/2011] [Indexed: 12/22/2022] Open
Abstract
Life is an inordinately complex unsolved puzzle. Despite significant theoretical progress, experimental anomalies, paradoxes, and enigmas have revealed paradigmatic limitations. Thus, the advancement of scientific understanding requires new models that resolve fundamental problems. Here, I present a theoretical framework that economically fits evidence accumulated from examinations of life. This theory is based upon a straightforward and non-mathematical core model and proposes unique yet empirically consistent explanations for major phenomena including, but not limited to, quantum gravity, phase transitions of water, why living systems are predominantly CHNOPS (carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur), homochirality of sugars and amino acids, homeoviscous adaptation, triplet code, and DNA mutations. The theoretical framework unifies the macrocosmic and microcosmic realms, validates predicted laws of nature, and solves the puzzle of the origin and evolution of cellular life in the universe.
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Affiliation(s)
- Erik D Andrulis
- Department of Molecular Biology and Microbiology, Case Western Reserve University School of Medicine, Wood Building, W212, Cleveland, OH 44106, USA.
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29
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Regulation of alternative splicing within the supraspliceosome. J Struct Biol 2011; 177:152-9. [PMID: 22100336 DOI: 10.1016/j.jsb.2011.11.005] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2011] [Revised: 11/02/2011] [Accepted: 11/05/2011] [Indexed: 12/12/2022]
Abstract
Alternative splicing is a fundamental feature in regulating the eukaryotic transcriptome, as ~95% of multi-exon human Pol II transcripts are subject to this process. Regulated splicing operates through the combinatorial interplay of positive and negative regulatory signals present in the pre-mRNA, which are recognized by trans-acting factors. All these RNA and protein components are assembled in a gigantic, 21 MDa, ribonucleoprotein splicing machine - the supraspliceosome. Because most alternatively spliced mRNA isoforms vary between different cell and tissue types, the ability to perform alternative splicing is expected to be an integral part of the supraspliceosome, which constitutes the splicing machine in vivo. Here we show that both the constitutively and alternatively spliced mRNAs of the endogenous human pol II transcripts: hnRNP A/B, survival of motor neuron (SMN) and ADAR2 are predominantly found in supraspliceosomes. This finding is consistent with our observations that the splicing regulators hnRNP G as well as all phosphorylated SR proteins are predominantly associated with supraspliceosomes. We further show that changes in alternative splicing of hnRNP A/B, affected by up regulation of SRSF5 (SRp40) or by treatment with C6-ceramide, occur within supraspliceosomes. These observations support the proposed role of the supraspliceosome in splicing regulation and alternative splicing.
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30
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Abstract
Pre-mRNA splicing is catalyzed by the spliceosome, a multimegadalton ribonucleoprotein (RNP) complex comprised of five snRNPs and numerous proteins. Intricate RNA-RNA and RNP networks, which serve to align the reactive groups of the pre-mRNA for catalysis, are formed and repeatedly rearranged during spliceosome assembly and catalysis. Both the conformation and composition of the spliceosome are highly dynamic, affording the splicing machinery its accuracy and flexibility, and these remarkable dynamics are largely conserved between yeast and metazoans. Because of its dynamic and complex nature, obtaining structural information about the spliceosome represents a major challenge. Electron microscopy has revealed the general morphology of several spliceosomal complexes and their snRNP subunits, and also the spatial arrangement of some of their components. X-ray and NMR studies have provided high resolution structure information about spliceosomal proteins alone or complexed with one or more binding partners. The extensive interplay of RNA and proteins in aligning the pre-mRNA's reactive groups, and the presence of both RNA and protein at the core of the splicing machinery, suggest that the spliceosome is an RNP enzyme. However, elucidation of the precise nature of the spliceosome's active site, awaits the generation of a high-resolution structure of its RNP core.
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Affiliation(s)
- Cindy L Will
- Max Planck Institute for Biophysical Chemistry, Department of Cellular Biochemistry, Am Fassberg 11, 37077 Göttingen, Germany
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31
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Huang T, Shaikh TR, Gupta K, Contreras-Martin LM, Grassucci RA, Van Duyne GD, Frank J, Belfort M. The group II intron ribonucleoprotein precursor is a large, loosely packed structure. Nucleic Acids Res 2010; 39:2845-54. [PMID: 21131279 PMCID: PMC3074136 DOI: 10.1093/nar/gkq1202] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Group II self-splicing introns are phylogenetically diverse retroelements that are widely held to be the ancestors of spliceosomal introns and retrotransposons that insert into DNA. Folding of group II intron RNA is often guided by an intron-encoded protein to form a catalytically active ribonucleoprotein (RNP) complex that plays a key role in the activity of the intron. To date, possible structural differences between the intron RNP in its precursor and spliced forms remain unexplored. In this work, we have trapped the native Lactococcus lactis group II intron RNP complex in its precursor form, by deleting the adenosine nucleophile that initiates splicing. Sedimentation velocity, size-exclusion chromatography and cryo-electron microscopy provide the first glimpse of the intron RNP precursor as a large, loosely packed structure. The dimensions contrast with those of compact spliced introns, implying that the RNP undergoes a dramatic conformational change to achieve the catalytically active state.
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Affiliation(s)
- Tao Huang
- Wadsworth Center, New York State Department of Health, Center for Medical Sciences, 150 New Scotland Avenue, Albany, NY 12201-2002, USA
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32
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A potential role for initiator-tRNA in pre-mRNA splicing regulation. Proc Natl Acad Sci U S A 2010; 107:11319-24. [PMID: 20534564 DOI: 10.1073/pnas.0911561107] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
The translation initiator-tRNA plays a crucial role in the initiation of protein synthesis in both prokaryotic and eukaryotic cells, by employing specific base pairing between its anticodon triplet CAU and the general initiation codon AUG in the mRNA. Here we show that the initiator-tRNA may also act, in a manner that is independent of its role in protein translation, as a pre-mRNA splicing regulator. Specifically, we show that alternative splicing events that are induced by mutations in the translation initiation AUG codon can be suppressed by expressing initiator-tRNA constructs carrying anticodon mutations that compensate for the AUG mutations. These mutated initiator-tRNAs appeared to be uncharged with an amino acid. Our results imply that recognition of the initiation AUG sequence by the anticodon triplet of initiator-tRNA in its unloaded state plays a role in quality control of splicing in the cell nucleus by a yet unresolved mechanism. Identifying the initiator-tRNA as a transacting splicing regulator suggests a novel involvement of this molecule in splicing regulation and provides a critical step toward deciphering this intriguing mechanism.
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33
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Krummel DAP, Nagai K, Oubridge C. Structure of spliceosomal ribonucleoproteins. F1000 BIOLOGY REPORTS 2010; 2:39. [PMID: 20948795 PMCID: PMC2950031 DOI: 10.3410/b2-39] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Splicing of the precursors of eukaryotic mRNA and some non-coding RNAs is catalyzed by the 'spliceosome', which comprises five RNA-protein complexes (small nuclear ribonucleoproteins, or snRNPs) that assemble in an ordered manner onto precursor-mRNAs. Much progress has been made in determining the gross morphology of spliceosomal assembly intermediates. Recently, the first crystal structure of a spliceosomal snRNP has provided significant insight into assembly and architecture of spliceosomal snRNPs in general and the structure-function relationship of human U1 snRNP in particular.
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Affiliation(s)
| | - Kiyoshi Nagai
- Medical Research Council Laboratory of Molecular BiologyHills Road, Cambridge, CB2 0QHUK
| | - Chris Oubridge
- Medical Research Council Laboratory of Molecular BiologyHills Road, Cambridge, CB2 0QHUK
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34
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Abstract
Lipid monolayers have traditionally been used in electron microscopy (EM) to form two-dimensional (2D) protein arrays for structural studies by electron crystallography. More recently, monolayers containing Nickel-nitrilotriacetic acid (Ni-NTA) lipids have been used to combine the purification and preparation of single-particle EM specimens of His-tagged proteins into a single, convenient step. This monolayer purification technique was further simplified by introducing the Affinity Grid, an EM grid that features a predeposited Ni-NTA lipid-containing monolayer. In this contribution, we provide a detailed description for the use of monolayer purification and Affinity Grids, discuss their advantages and limitations, and present examples to illustrate specific applications of the methods.
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35
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Wong H, Winn PJ, Mozziconacci J. A molecular model of chromatin organisation and transcription:how a multi-RNA polymerase II machine transcribes and remodels the β-globin locus during development. Bioessays 2009; 31:1357-66. [DOI: 10.1002/bies.200900062] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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36
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Heinrich B, Zhang Z, Raitskin O, Hiller M, Benderska N, Hartmann AM, Bracco L, Elliott D, Ben-Ari S, Soreq H, Sperling J, Sperling R, Stamm S. Heterogeneous nuclear ribonucleoprotein G regulates splice site selection by binding to CC(A/C)-rich regions in pre-mRNA. J Biol Chem 2009; 284:14303-15. [PMID: 19282290 PMCID: PMC2682879 DOI: 10.1074/jbc.m901026200] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2009] [Revised: 03/11/2009] [Indexed: 11/06/2022] Open
Abstract
Almost every protein-coding gene undergoes pre-mRNA splicing, and the majority of these pre-mRNAs are alternatively spliced. Alternative exon usage is regulated by the transient formation of protein complexes on the pre-mRNA that typically contain heterogeneous nuclear ribonucleoproteins (hnRNPs). Here we characterize hnRNP G, a member of the hnRNP class of proteins. We show that hnRNP G is a nuclear protein that is expressed in different concentrations in various tissues and that interacts with other splicing regulatory proteins. hnRNP G is part of the supraspliceosome, where it regulates alternative splice site selection in a concentration-dependent manner. Its action on alternative exons can occur without a functional RNA-recognition motif by binding to other splicing regulatory proteins. The RNA-recognition motif of hnRNP G binds to a loose consensus sequence containing a CC(A/C) motif, and hnRNP G preferentially regulates alternative exons where this motif is clustered in close proximity. The X-chromosomally encoded hnRNP G regulates different RNAs than its Y-chromosomal paralogue RNA-binding motif protein, Y-linked (RBMY), suggesting that differences in alternative splicing, evoked by the sex-specific expression of hnRNP G and RBMY, could contribute to molecular sex differences in mammals.
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Affiliation(s)
- Bettina Heinrich
- Institute for Biochemistry, University of Erlangen, Fahrstrasse 17, 91054 Erlangen, Germany
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37
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Lührmann R, Stark H. Structural mapping of spliceosomes by electron microscopy. Curr Opin Struct Biol 2009; 19:96-102. [DOI: 10.1016/j.sbi.2009.01.001] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2008] [Revised: 01/06/2009] [Accepted: 01/07/2009] [Indexed: 10/21/2022]
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38
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Sperling J, Azubel M, Sperling R. Structure and function of the Pre-mRNA splicing machine. Structure 2009; 16:1605-15. [PMID: 19000813 DOI: 10.1016/j.str.2008.08.011] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2008] [Revised: 08/22/2008] [Accepted: 08/27/2008] [Indexed: 12/14/2022]
Abstract
Most eukaryotic pre-mRNAs contain non-coding sequences (introns) that must be removed in order to accurately place the coding sequences (exons) in the correct reading frame. This critical regulatory pre-mRNA splicing event is fundamental in development and cancer. It occurs within a mega-Dalton multicomponent machine composed of RNA and proteins, which undergoes dynamic changes in RNA-RNA, RNA-protein, and protein-protein interactions during the splicing reaction. Recent years have seen progress in functional and structural analyses of the splicing machine and its subcomponents, and this review is focused on structural aspects of the pre-mRNA splicing machine and their mechanistic implications on the splicing of multi-intronic pre-mRNAs. It brings together, in a comparative manner, structural information on spliceosomes and their intermediates in the stepwise assembly process in vitro, and on the preformed supraspliceosomes, which are isolated from living cell nuclei, with a view of portraying a consistent picture.
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Affiliation(s)
- Joseph Sperling
- Department of Organic Chemistry, The Weizmann Institute of Science, Rehovot 76100, Israel
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39
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The editing enzyme ADAR1 and the mRNA surveillance protein hUpf1 interact in the cell nucleus. Proc Natl Acad Sci U S A 2008; 105:5028-33. [PMID: 18362360 DOI: 10.1073/pnas.0710576105] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Posttranscriptional regulation is an important step in the regulation of gene expression. In this article, we show an unexpected connection between two proteins that participate in different processes of posttranscriptional regulation that ensures the production of functional mRNA molecules. Specifically, we show that the A-to-I RNA editing protein adenosine deaminase that acts on RNA 1 (ADAR1) and the human Upf1 (hUpf1) protein involved in RNA surveillance are found associated within nuclear RNA-splicing complexes. A potential functional role for this association was revealed by RNAi-mediated down-regulation of ADAR1, which was accompanied by up-regulation of a number of genes previously shown to undergo A-to-I editing in Alu repeats and to be down-regulated by hUpf1. This study suggests a regulatory pathway by a combination of ADAR1 A-to-I editing enzyme and RNA degradation presumably with the aid of hUpf1.
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40
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Monolayer purification: a rapid method for isolating protein complexes for single-particle electron microscopy. Proc Natl Acad Sci U S A 2008; 105:4703-8. [PMID: 18347330 DOI: 10.1073/pnas.0800867105] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Visualizing macromolecular complexes by single-particle electron microscopy (EM) entails stringent biochemical purification, specimen preparation, low-dose imaging, and 3D image reconstruction. Here, we introduce the "monolayer purification" method, which employs nickel-nitrilotriacetic acid (Ni-NTA) functionalized lipids for simultaneously purifying His-tagged complexes directly from cell lysates while producing specimens suitable for single-particle EM. The method was established by using monolayers containing Ni-NTA lipid to specifically adsorb His-tagged transferrin-transferrin receptor (Tf-TfR) complexes from insect and mammalian cell extracts. The specificity and sensitivity of the method could be improved by adding imidazole to the extracts. The monolayer-purified Tf-TfR samples could be vitrified and used to calculate a 3D reconstruction of the complex. Monolayer purification was then used to rapidly isolate ribosomal complexes from bacteria by overexpressing a single His-tagged ribosomal subunit. The resulting monolayer samples allowed calculation of a cryo-EM 3D reconstruction of the Escherichia coli 50S ribosomal subunit.
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41
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A new cryo-EM single-particle ab initio reconstruction method visualizes secondary structure elements in an ATP-fueled AAA+ motor. J Mol Biol 2007; 375:934-47. [PMID: 18068723 DOI: 10.1016/j.jmb.2007.11.028] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2007] [Revised: 11/01/2007] [Accepted: 11/09/2007] [Indexed: 11/22/2022]
Abstract
The generation of ab initio three-dimensional (3D) models is a bottleneck in the studies of large macromolecular assemblies by single-particle cryo-electron microscopy. We describe here a novel method, in which established methods for two-dimensional image processing are combined with newly developed programs for joint rotational 3D alignment of a large number of class averages (RAD) and calculation of 3D volumes from aligned projections (VolRec). We demonstrate the power of the method by reconstructing an approximately 660-kDa ATP-fueled AAA+ motor to 7.5 A resolution, with secondary structure elements identified throughout the structure. We propose the method as a generally applicable automated strategy to obtain 3D reconstructions from unstained single particles imaged in vitreous ice.
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42
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Chen YIG, Moore RE, Ge HY, Young MK, Lee TD, Stevens SW. Proteomic analysis of in vivo-assembled pre-mRNA splicing complexes expands the catalog of participating factors. Nucleic Acids Res 2007; 35:3928-44. [PMID: 17537823 PMCID: PMC1919476 DOI: 10.1093/nar/gkm347] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Previous compositional studies of pre-mRNA processing complexes have been performed in vitro on synthetic pre-mRNAs containing a single intron. To provide a more comprehensive list of polypeptides associated with the pre-mRNA splicing apparatus, we have determined the composition of the bulk pre-mRNA processing machinery in living cells. We purified endogenous nuclear pre-mRNA processing complexes from human and chicken cells comprising the massive (>200S) supraspliceosomes (a.k.a. polyspliceosomes). As expected, RNA components include a heterogeneous mixture of pre-mRNAs and the five spliceosomal snRNAs. In addition to known pre-mRNA splicing factors, 5′ end binding factors, 3′ end processing factors, mRNA export factors, hnRNPs and other RNA binding proteins, the protein components identified by mass spectrometry include RNA adenosine deaminases and several novel factors. Intriguingly, our purified supraspliceosomes also contain a number of structural proteins, nucleoporins, chromatin remodeling factors and several novel proteins that were absent from splicing complexes assembled in vitro. These in vivo analyses bring the total number of factors associated with pre-mRNA to well over 300, and represent the most comprehensive analysis of the pre-mRNA processing machinery to date.
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Affiliation(s)
- Yen-I G. Chen
- Graduate program in Microbiology, City of Hope Beckman Research Institute, Duarte, CA 91010, Section of Molecular Genetics and Microbiology, University of Texas at Austin, 1 University, Station #A4800, Austin, TX 78712 and Institute for Cellular and Molecular Biology, University of Texas at Austin, TX, USA
| | - Roger E. Moore
- Graduate program in Microbiology, City of Hope Beckman Research Institute, Duarte, CA 91010, Section of Molecular Genetics and Microbiology, University of Texas at Austin, 1 University, Station #A4800, Austin, TX 78712 and Institute for Cellular and Molecular Biology, University of Texas at Austin, TX, USA
| | - Helen Y. Ge
- Graduate program in Microbiology, City of Hope Beckman Research Institute, Duarte, CA 91010, Section of Molecular Genetics and Microbiology, University of Texas at Austin, 1 University, Station #A4800, Austin, TX 78712 and Institute for Cellular and Molecular Biology, University of Texas at Austin, TX, USA
| | - Mary K. Young
- Graduate program in Microbiology, City of Hope Beckman Research Institute, Duarte, CA 91010, Section of Molecular Genetics and Microbiology, University of Texas at Austin, 1 University, Station #A4800, Austin, TX 78712 and Institute for Cellular and Molecular Biology, University of Texas at Austin, TX, USA
| | - Terry D. Lee
- Graduate program in Microbiology, City of Hope Beckman Research Institute, Duarte, CA 91010, Section of Molecular Genetics and Microbiology, University of Texas at Austin, 1 University, Station #A4800, Austin, TX 78712 and Institute for Cellular and Molecular Biology, University of Texas at Austin, TX, USA
| | - Scott W. Stevens
- Graduate program in Microbiology, City of Hope Beckman Research Institute, Duarte, CA 91010, Section of Molecular Genetics and Microbiology, University of Texas at Austin, 1 University, Station #A4800, Austin, TX 78712 and Institute for Cellular and Molecular Biology, University of Texas at Austin, TX, USA
- *To whom correspondence should be addressed. +1-512-232-9303+1-512-232-3432
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43
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Taylor DW, Kelly DF, Cheng A, Taylor KA. On the freezing and identification of lipid monolayer 2-D arrays for cryoelectron microscopy. J Struct Biol 2007; 160:305-12. [PMID: 17561414 PMCID: PMC2268103 DOI: 10.1016/j.jsb.2007.04.011] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2005] [Revised: 04/02/2007] [Accepted: 04/04/2007] [Indexed: 11/22/2022]
Abstract
Lipid monolayers provide a convenient vehicle for the crystallization of biological macromolecules for 3-D electron microscopy. Although numerous examples of 3-D images from 2-D protein arrays have been described from negatively stained specimens, only six structures have been done from frozen-hydrated specimens. We describe here a method that makes high quality frozen-hydrated specimens of lipid monolayer arrays for cryoelectron microscopy. The method uses holey carbon films with patterned holes for monolayer recovery, blotting and plunge freezing to produce thin aqueous films which cover >90% of the available grid area. With this method, even specimens with relatively infrequent crystals can be screened using automated data collection techniques. Though developed for microscopic examination of 2-D arrays, the method may have wider application to the preparation of single particle specimens for 3-D image reconstruction.
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Affiliation(s)
- Dianne W Taylor
- Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306-4380, USA.
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44
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Behzadnia N, Golas MM, Hartmuth K, Sander B, Kastner B, Deckert J, Dube P, Will CL, Urlaub H, Stark H, Lührmann R. Composition and three-dimensional EM structure of double affinity-purified, human prespliceosomal A complexes. EMBO J 2007; 26:1737-48. [PMID: 17332742 PMCID: PMC1829389 DOI: 10.1038/sj.emboj.7601631] [Citation(s) in RCA: 154] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2006] [Accepted: 02/02/2007] [Indexed: 11/09/2022] Open
Abstract
Little is known about the higher-order structure of prespliceosomal A complexes, in which pairing of the pre-mRNA's splice sites occurs. Here, human A complexes were isolated under physiological conditions by double-affinity selection. Purified complexes contained stoichiometric amounts of U1, U2 and pre-mRNA, and crosslinking studies indicated that these form concomitant base pairing interactions with one another. A complexes contained nearly all U1 and U2 proteins plus approximately 50 non-snRNP proteins. Unexpectedly, proteins of the hPrp19/CDC5 complex were also detected, even when A complexes were formed in the absence of U4/U6 snRNPs, demonstrating that they associate independent of the tri-snRNP. Double-affinity purification yielded structurally homogeneous A complexes as evidenced by electron microscopy, and allowed for the first time the generation of a three-dimensional structure. A complexes possess an asymmetric shape (approximately 260 x 200 x 195 angstroms) and contain a main body with various protruding elements, including a head-like domain and foot-like protrusions. Complexes isolated here are well suited for in vitro assembly studies to determine factor requirements for the A to B complex transition.
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Affiliation(s)
- Nastaran Behzadnia
- Department of Cellular Biochemistry, MPI of Biophysical Chemistry, Göttingen, Germany
| | - Monika M Golas
- 3D Electron Cryomicroscopy Group, MPI of Biophysical Chemistry, Göttingen, Germany
| | - Klaus Hartmuth
- Department of Cellular Biochemistry, MPI of Biophysical Chemistry, Göttingen, Germany
| | - Bjoern Sander
- 3D Electron Cryomicroscopy Group, MPI of Biophysical Chemistry, Göttingen, Germany
| | - Berthold Kastner
- Department of Cellular Biochemistry, MPI of Biophysical Chemistry, Göttingen, Germany
| | - Jochen Deckert
- Department of Cellular Biochemistry, MPI of Biophysical Chemistry, Göttingen, Germany
| | - Prakash Dube
- 3D Electron Cryomicroscopy Group, MPI of Biophysical Chemistry, Göttingen, Germany
| | - Cindy L Will
- Department of Cellular Biochemistry, MPI of Biophysical Chemistry, Göttingen, Germany
| | - Henning Urlaub
- Bioanalytical Mass Spectrometry Group, MPI of Biophysical Chemistry, Göttingen, Germany
| | - Holger Stark
- 3D Electron Cryomicroscopy Group, MPI of Biophysical Chemistry, Göttingen, Germany
- 3D Electron Cryomicroscopy Group, MPI for Biophysical Chemistry, Am Fassberg 11, Göttingen 37077, Germany. Tel.: +49 551 2011305; Fax: +49 551 2011197; E-mail:
| | - Reinhard Lührmann
- Department of Cellular Biochemistry, MPI of Biophysical Chemistry, Göttingen, Germany
- Department of Cellular Biochemistry, MPI for Biophysical Chemistry, Am Fassberg 11, Göttingen 37077, Germany. Tel.: +49 551 2011407; Fax: +49 551 2011197; E-mail:
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45
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Ohi MD, Ren L, Wall JS, Gould KL, Walz T. Structural characterization of the fission yeast U5.U2/U6 spliceosome complex. Proc Natl Acad Sci U S A 2007; 104:3195-200. [PMID: 17360628 PMCID: PMC1805518 DOI: 10.1073/pnas.0611591104] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The spliceosome is a dynamic macromolecular machine that catalyzes the excision of introns from pre-mRNA. The megadalton-sized spliceosome is composed of four small nuclear RNPs and additional pre-mRNA splicing factors. The formation of an active spliceosome involves a series of regulated steps that requires the assembly and disassembly of large multiprotein/RNA complexes. The dynamic nature of the pre-mRNA splicing reaction has hampered progress in analyzing the structure of spliceosomal complexes. We have used cryo-electron microscopy to produce a 29-A density map of a stable 37S spliceosomal complex from the genetically tractable fission yeast, Schizosaccharomyces pombe. Containing the U2, U5, and U6 snRNAs, pre-mRNA splicing intermediates, U2 and U5 snRNP proteins, the Nineteen Complex (NTC), and second-step splicing factors, this complex closely resembles in vitro purified mammalian C complex. The density map reveals an asymmetric particle, approximately 30 x 20 x 18 nm in size, which is composed of distinct domains that contact each other at the center of the complex.
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Affiliation(s)
- Melanie D. Ohi
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115
| | - Liping Ren
- Howard Hughes Medical Institute and
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN 37232; and
| | - Joseph S. Wall
- Biology Department, Brookhaven National Laboratory, Upton, NY 11973
| | - Kathleen L. Gould
- Howard Hughes Medical Institute and
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN 37232; and
- To whom correspondence may be addressed. E-mail: or
| | - Thomas Walz
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115
- To whom correspondence may be addressed. E-mail: or
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46
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Cohen-Krausz S, Sperling R, Sperling J. Exploring the architecture of the intact supraspliceosome using electron microscopy. J Mol Biol 2007; 368:319-27. [PMID: 17359996 DOI: 10.1016/j.jmb.2007.01.090] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2006] [Revised: 12/19/2006] [Accepted: 01/31/2007] [Indexed: 11/20/2022]
Abstract
Splicing of pre-mRNA takes place on a massive macromolecular machine in the nucleus of eukaryotic cells, the supraspliceosome. This particle is a multicomponent biological complex of RNA and proteins. It is composed of four sub-structures termed native spliceosomes that splice pre-mRNA. The structure of the native spliceosome, determined by cryo-EM at 20 A resolution, showed that it is composed of two distinct subunits. Previously, medium resolution structural analysis of supraspliceosomes by electron tomography was performed, yet little is known of how the native spliceosomes are arranged within the intact particle. To address this question the native spliceosomes were analyzed and reconstructed in the context of the intact particle, using electron microscopy combined with image processing. Good correlation was obtained between the structure of the isolated native spliceosome, solved by cryo-EM, and the native spliceosome within the intact supraspliceosome. An ordered assembly was revealed with different potential roles assigned to the small and large subunits of the native spliceosome. The edges of the small subunits, which are in the center of the supraspliceosome, form a right angle and thus facilitate close contacts between the small subunits generating a 4-fold pattern. The analysis of sub-complex orientation within the particle suggests a possible route within the supraspliceosome for the passage of pre-mRNA, which is known to hold the particle together.
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Affiliation(s)
- Sara Cohen-Krausz
- Department of Organic Chemistry, Weizmann Institute of Science, Rehovot, Israel
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47
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Sander B, Golas MM, Makarov EM, Brahms H, Kastner B, Lührmann R, Stark H. Organization of core spliceosomal components U5 snRNA loop I and U4/U6 Di-snRNP within U4/U6.U5 Tri-snRNP as revealed by electron cryomicroscopy. Mol Cell 2006; 24:267-78. [PMID: 17052460 DOI: 10.1016/j.molcel.2006.08.021] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2006] [Revised: 07/18/2006] [Accepted: 08/22/2006] [Indexed: 11/27/2022]
Abstract
In eukaryotes, pre-mRNA exons are interrupted by large noncoding introns. Alternative selection of exons and nucleotide-exact removal of introns are performed by the spliceosome, a highly dynamic macromolecular machine. U4/U6.U5 tri-snRNP is the largest and most conserved building block of the spliceosome. By 3D electron cryomicroscopy and labeling, the exon-aligning U5 snRNA loop I is localized at the center of the tetrahedrally shaped tri-snRNP reconstructed to approximately 2.1 nm resolution in vitrified ice. Independent 3D reconstructions of its subunits, U4/U6 and U5 snRNPs, show how U4/U6 and U5 combine to form tri-snRNP and, together with labeling experiments, indicate a close proximity of the spliceosomal core components U5 snRNA loop I and U4/U6 at the center of tri-snRNP. We suggest that this central tri-snRNP region may be the site to which the prespliceosomal U2 snRNA has to approach closely during formation of the catalytic core of the spliceosome.
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Affiliation(s)
- Bjoern Sander
- Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
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48
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Montaville P, Dai Y, Cheung CY, Giller K, Becker S, Michalak M, Webb SE, Miller AL, Krebs J. Nuclear translocation of the calcium-binding protein ALG-2 induced by the RNA-binding protein RBM22. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2006; 1763:1335-43. [PMID: 17045351 DOI: 10.1016/j.bbamcr.2006.09.003] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/18/2006] [Revised: 08/31/2006] [Accepted: 09/01/2006] [Indexed: 11/15/2022]
Abstract
By yeast two-hybrid screening using the calcium-binding protein ALG-2 as bait a new target of ALG-2 was identified, the RNA-binding protein RBM22. In order to confirm these interactions in vivo we prepared fluorescent constructs by using the monomeric red fluorescent protein to label ALG-2 and the enhanced green fluorescent protein to label RBM22. Confocal microscopy of NIH 3T3 cells transfected with either ALG-2 or RBM22 expression constructs encoding fluorescent fusion proteins alone revealed that the majority of ALG-2 was localized in the cytoplasm whereas RBM22 was located in the nucleus. When cells were co-transfected with expression vectors encoding both fusion proteins ALG-2 was found in the nucleus indicating that RBM22 which can shuttle between the cytoplasm and the nucleus may play a role in nuclear translocation of ALG-2. Using zebrafish as a model mRNA homologues of ALG-2 and RBM22 were microinjected into the blastodisc-yolk margin of zebrafish embryos at the 1-cell stage followed by monitoring the fusion proteins during development of the zebrafish. Hereby, we observed that ALG-2 alone evenly distributed within the cell, whereas in the presence of RBM22 the two proteins co-localized within the nucleus. More than 95% of the two proteins co-localized within the same area in the nucleus suggesting a functional interaction between the Ca(2+)-signaling protein ALG-2 and the RNA-binding protein RBM22.
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Affiliation(s)
- P Montaville
- Department of NMR-based Structural Biology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
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49
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Markus MA, Heinrich B, Raitskin O, Adams DJ, Mangs H, Goy C, Ladomery M, Sperling R, Stamm S, Morris BJ. WT1 interacts with the splicing protein RBM4 and regulates its ability to modulate alternative splicing in vivo. Exp Cell Res 2006; 312:3379-88. [PMID: 16934801 DOI: 10.1016/j.yexcr.2006.07.008] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2006] [Revised: 06/26/2006] [Accepted: 07/17/2006] [Indexed: 10/24/2022]
Abstract
Wilm's tumor protein 1 (WT1), a protein implicated in various cancers and developmental disorders, consists of two major isoforms: WT1(-KTS), a transcription factor, and WT1(+KTS), a post-transcriptional regulator that binds to RNA and can interact with splicing components. Here we show that WT1 interacts with the novel splicing regulator RBM4. Each protein was found to colocalize in nuclear speckles and to cosediment with supraspliceosomes in glycerol gradients. RBM4 conferred dose-dependent and cell-specific regulation of alternative splicing of pre-mRNAs transcribed from several reporter genes. We found that overexpressed WT1(+KTS) abrogated this effect of RBM4 on splice-site selection, whereas WT1(-KTS) did not. We conclude that the (+KTS) form of WT1 is able to inhibit the effect of RBM4 on alternative splicing.
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Affiliation(s)
- M Andrea Markus
- Basic & Clinical Genomics Laboratory, School of Medical Sciences and Bosch Institute, Building F13, The University of Sydney, NSW 2006, Australia
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Deckert J, Hartmuth K, Boehringer D, Behzadnia N, Will CL, Kastner B, Stark H, Urlaub H, Lührmann R. Protein composition and electron microscopy structure of affinity-purified human spliceosomal B complexes isolated under physiological conditions. Mol Cell Biol 2006; 26:5528-43. [PMID: 16809785 PMCID: PMC1592722 DOI: 10.1128/mcb.00582-06] [Citation(s) in RCA: 224] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The spliceosomal B complex is the substrate that undergoes catalytic activation leading to catalysis of pre-mRNA splicing. Previous characterization of this complex was performed in the presence of heparin, which dissociates less stably associated components. To obtain a more comprehensive inventory of the B complex proteome, we isolated this complex under low-stringency conditions using two independent methods. MS2 affinity-selected B complexes supported splicing when incubated in nuclear extract depleted of snRNPs. Mass spectrometry identified over 110 proteins in both independently purified B complex preparations, including approximately 50 non-snRNP proteins not previously found in the spliceosomal A complex. Unexpectedly, the heteromeric hPrp19/CDC5 complex and 10 additional hPrp19/CDC5-related proteins were detected, indicating that they are recruited prior to spliceosome activation. Electron microscopy studies revealed that MS2 affinity-selected B complexes exhibit a rhombic shape with a maximum dimension of 420 A and are structurally more homogeneous than B complexes treated with heparin. These data provide novel insights into the composition and structure of the spliceosome just prior to its catalytic activation and suggest a potential role in activation for proteins recruited at this stage. Furthermore, the spliceosomal complexes isolated here are well suited for complementation studies with purified proteins to dissect factor requirements for spliceosome activation and splicing catalysis.
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Affiliation(s)
- Jochen Deckert
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
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