1
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Shen A, Hencel K, Parker MT, Scott R, Skukan R, Adesina AS, Metheringham CL, Miska EA, Nam Y, Haerty W, Simpson GG, Akay A. U6 snRNA m6A modification is required for accurate and efficient splicing of C. elegans and human pre-mRNAs. Nucleic Acids Res 2024:gkae447. [PMID: 38808663 DOI: 10.1093/nar/gkae447] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2023] [Revised: 05/08/2024] [Accepted: 05/13/2024] [Indexed: 05/30/2024] Open
Abstract
pre-mRNA splicing is a critical feature of eukaryotic gene expression. Both cis- and trans-splicing rely on accurately recognising splice site sequences by spliceosomal U snRNAs and associated proteins. Spliceosomal snRNAs carry multiple RNA modifications with the potential to affect different stages of pre-mRNA splicing. Here, we show that the conserved U6 snRNA m6A methyltransferase METT-10 is required for accurate and efficient cis- and trans-splicing of C. elegans pre-mRNAs. The absence of METT-10 in C. elegans and METTL16 in humans primarily leads to alternative splicing at 5' splice sites with an adenosine at +4 position. In addition, METT-10 is required for splicing of weak 3' cis- and trans-splice sites. We identified a significant overlap between METT-10 and the conserved splicing factor SNRNP27K in regulating 5' splice sites with +4A. Finally, we show that editing endogenous 5' splice site +4A positions to +4U restores splicing to wild-type positions in a mett-10 mutant background, supporting a direct role for U6 snRNA m6A modification in 5' splice site recognition. We conclude that the U6 snRNA m6A modification is important for accurate and efficient pre-mRNA splicing.
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Affiliation(s)
- Aykut Shen
- School of Biological Sciences, University of East Anglia, NR4 7TJ Norwich, UK
| | - Katarzyna Hencel
- School of Biological Sciences, University of East Anglia, NR4 7TJ Norwich, UK
| | - Matthew T Parker
- School of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - Robyn Scott
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Roberta Skukan
- School of Biological Sciences, University of East Anglia, NR4 7TJ Norwich, UK
| | | | | | - Eric A Miska
- Wellcome/CRUK Gurdon Institute, University of Cambridge, Tennis Court Rd, Cambridge CB2 1QN, UK
| | - Yunsun Nam
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX, USA
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA
- Simmons Comprehensive Cancer Center, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Wilfried Haerty
- School of Biological Sciences, University of East Anglia, NR4 7TJ Norwich, UK
- Earlham Institute, Norwich Research Park, Norwich, UK
| | - Gordon G Simpson
- School of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK
- Cell & Molecular Sciences, James Hutton Institute, Invergowrie, DD2 5DA, UK
| | - Alper Akay
- School of Biological Sciences, University of East Anglia, NR4 7TJ Norwich, UK
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2
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Su Y, Wu J, Chen W, Shan J, Chen D, Zhu G, Ge S, Liu Y. Spliceosomal snRNAs, the Essential Players in pre-mRNA Processing in Eukaryotic Nucleus: From Biogenesis to Functions and Spatiotemporal Characteristics. Adv Biol (Weinh) 2024:e2400006. [PMID: 38797893 DOI: 10.1002/adbi.202400006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2024] [Revised: 04/30/2024] [Indexed: 05/29/2024]
Abstract
Spliceosomal small nuclear RNAs (snRNAs) are a fundamental class of non-coding small RNAs abundant in the nucleoplasm of eukaryotic cells, playing a crucial role in splicing precursor messenger RNAs (pre-mRNAs). They are transcribed by DNA-dependent RNA polymerase II (Pol II) or III (Pol III), and undergo subsequent processing and 3' end cleavage to become mature snRNAs. Numerous protein factors are involved in the transcription initiation, elongation, termination, splicing, cellular localization, and terminal modification processes of snRNAs. The transcription and processing of snRNAs are regulated spatiotemporally by various mechanisms, and the homeostatic balance of snRNAs within cells is of great significance for the growth and development of organisms. snRNAs assemble with specific accessory proteins to form small nuclear ribonucleoprotein particles (snRNPs) that are the basal components of spliceosomes responsible for pre-mRNA maturation. This article provides an overview of the biological functions, biosynthesis, terminal structure, and tissue-specific regulation of snRNAs.
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Affiliation(s)
- Yuan Su
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, College of Life Science and Technology, Guangxi University, Nanning, Guangxi, 530004, China
| | - Jiaming Wu
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, College of Life Science and Technology, Guangxi University, Nanning, Guangxi, 530004, China
| | - Wei Chen
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, College of Life Science and Technology, Guangxi University, Nanning, Guangxi, 530004, China
| | - Junling Shan
- Department of basic medicine, Guangxi Medical University of Nursing College, Nanning, Guangxi, 530021, China
| | - Dan Chen
- Ruikang Hospital Affiliated to Guangxi University of Chinese Medicine, Nanning, Guangxi, 530011, China
| | - Guangyu Zhu
- Guangxi Medical University Hospital of Stomatology, Nanning, Guangxi, 530021, China
| | - Shengchao Ge
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, College of Life Science and Technology, Guangxi University, Nanning, Guangxi, 530004, China
| | - Yunfeng Liu
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, College of Life Science and Technology, Guangxi University, Nanning, Guangxi, 530004, China
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3
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Shen A, Hencel K, Parker MT, Scott R, Skukan R, Adesina AS, Metheringham CL, Miska EA, Nam Y, Haerty W, Simpson GG, Akay A. U6 snRNA m6A modification is required for accurate and efficient cis- and trans-splicing of C. elegans mRNAs. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.09.16.558044. [PMID: 37745402 PMCID: PMC10516052 DOI: 10.1101/2023.09.16.558044] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/26/2023]
Abstract
pre-mRNA splicing is a critical feature of eukaryotic gene expression. Many eukaryotes use cis-splicing to remove intronic sequences from pre-mRNAs. In addition to cis-splicing, many organisms use trans-splicing to replace the 5' ends of mRNAs with a non-coding spliced-leader RNA. Both cis- and trans-splicing rely on accurately recognising splice site sequences by spliceosomal U snRNAs and associated proteins. Spliceosomal snRNAs carry multiple RNA modifications with the potential to affect different stages of pre-mRNA splicing. Here, we show that m6A modification of U6 snRNA A43 by the RNA methyltransferase METT-10 is required for accurate and efficient cis- and trans-splicing of C. elegans pre-mRNAs. The absence of U6 snRNA m6A modification primarily leads to alternative splicing at 5' splice sites. Furthermore, weaker 5' splice site recognition by the unmodified U6 snRNA A43 affects splicing at 3' splice sites. U6 snRNA m6A43 and the splicing factor SNRNP27K function to recognise an overlapping set of 5' splice sites with an adenosine at +4 position. Finally, we show that U6 snRNA m6A43 is required for efficient SL trans-splicing at weak 3' trans-splice sites. We conclude that the U6 snRNA m6A modification is important for accurate and efficient cis- and trans-splicing in C. elegans.
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Affiliation(s)
- Aykut Shen
- School of Biological Sciences, University of East Anglia, NR4 7TJ, Norwich
| | - Katarzyna Hencel
- School of Biological Sciences, University of East Anglia, NR4 7TJ, Norwich
- These authors contributed equally
| | - Matthew T Parker
- School of Life Sciences, University of Dundee, Dow Street, Dundee, DD1 5EH, UK
- These authors contributed equally
| | - Robyn Scott
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Roberta Skukan
- School of Biological Sciences, University of East Anglia, NR4 7TJ, Norwich
| | | | | | - Eric A Miska
- Wellcome/CRUK Gurdon Institute, University of Cambridge, Tennis Court Rd, Cambridge, CB2 1QN, UK
| | - Yunsun Nam
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX, USA
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX, USA
- Simmons Comprehensive Cancer Center, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Wilfried Haerty
- School of Biological Sciences, University of East Anglia, NR4 7TJ, Norwich
- Earlham Institute, Norwich Research Park, Norwich, UK
| | - Gordon G Simpson
- School of Life Sciences, University of Dundee, Dow Street, Dundee, DD1 5EH, UK
- Cell & Molecular Sciences, James Hutton Institute, Invergowrie, DD2 5DA, UK
| | - Alper Akay
- School of Biological Sciences, University of East Anglia, NR4 7TJ, Norwich
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4
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Black CS, Whelan TA, Garside EL, MacMillan AM, Fast NM, Rader SD. Spliceosome assembly and regulation: insights from analysis of highly reduced spliceosomes. RNA (NEW YORK, N.Y.) 2023; 29:531-550. [PMID: 36737103 PMCID: PMC10158995 DOI: 10.1261/rna.079273.122] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2022] [Accepted: 01/06/2023] [Indexed: 05/06/2023]
Abstract
Premessenger RNA splicing is catalyzed by the spliceosome, a multimegadalton RNA-protein complex that assembles in a highly regulated process on each intronic substrate. Most studies of splicing and spliceosomes have been carried out in human or S. cerevisiae model systems. There exists, however, a large diversity of spliceosomes, particularly in organisms with reduced genomes, that suggests a means of analyzing the essential elements of spliceosome assembly and regulation. In this review, we characterize changes in spliceosome composition across phyla, describing those that are most frequently observed and highlighting an analysis of the reduced spliceosome of the red alga Cyanidioschyzon merolae We used homology modeling to predict what effect splicing protein loss would have on the spliceosome, based on currently available cryo-EM structures. We observe strongly correlated loss of proteins that function in the same process, for example, in interacting with the U1 snRNP (which is absent in C. merolae), regulation of Brr2, or coupling transcription and splicing. Based on our observations, we predict splicing in C. merolae to be inefficient, inaccurate, and post-transcriptional, consistent with the apparent trend toward its elimination in this lineage. This work highlights the striking flexibility of the splicing pathway and the spliceosome when viewed in the context of eukaryotic diversity.
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Affiliation(s)
- Corbin S Black
- Department of Chemistry and Biochemistry, University of Northern British Columbia, Prince George, British Columbia, Canada V2N 4Z9
- Department of Anatomy and Cell Biology, McGill University, Montréal, Quebec, Canada H3A 0C7
| | - Thomas A Whelan
- Biodiversity Research Center and Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4
| | - Erin L Garside
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
| | - Andrew M MacMillan
- Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
| | - Naomi M Fast
- Biodiversity Research Center and Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4
| | - Stephen D Rader
- Department of Chemistry and Biochemistry, University of Northern British Columbia, Prince George, British Columbia, Canada V2N 4Z9
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5
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Cao Y, Wang J, Wu S, Yin X, Shu J, Dai X, Liu Y, Sun L, Zhu D, Deng XW, Ye K, Qian W. The small nucleolar RNA SnoR28 regulates plant growth and development by directing rRNA maturation. THE PLANT CELL 2022; 34:4173-4190. [PMID: 36005862 PMCID: PMC9614442 DOI: 10.1093/plcell/koac265] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/08/2022] [Accepted: 08/11/2022] [Indexed: 06/15/2023]
Abstract
Small nucleolar RNAs (snoRNAs) are noncoding RNAs (ncRNAs) that guide chemical modifications of structural RNAs, which are essential for ribosome assembly and function in eukaryotes. Although numerous snoRNAs have been identified in plants by high-throughput sequencing, the biological functions of most of these snoRNAs remain unclear. Here, we identified box C/D SnoR28.1s as important regulators of plant growth and development by screening a CRISPR/Cas9-generated ncRNA deletion mutant library in Arabidopsis thaliana. Deletion of the SnoR28.1 locus, which contains a cluster of three genes producing SnoR28.1s, resulted in defects in root and shoot growth. SnoR28.1s guide 2'-O-ribose methylation of 25S rRNA at G2396. SnoR28.1s facilitate proper and efficient pre-rRNA processing, as the SnoR28.1 deletion mutants also showed impaired ribosome assembly and function, which may account for the growth defects. SnoR28 contains a 7-bp antisense box, which is required for 2'-O-ribose methylation of 25S rRNA at G2396, and an 8-bp extra box that is complementary to a nearby rRNA methylation site and is partially responsible for methylation of G2396. Both of these motifs are required for proper and efficient pre-rRNA processing. Finally, we show that SnoR28.1s genetically interact with HIDDEN TREASURE2 and NUCLEOLIN1. Our results advance our understanding of the roles of snoRNAs in Arabidopsis.
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Affiliation(s)
- Yuxin Cao
- State Key Laboratory of Protein and Plant Gene Research, School of Advanced Agricultural Sciences, Peking University, Beijing 100871, China
| | - Jiayin Wang
- Key Laboratory of RNA Biology, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Songlin Wu
- Key Laboratory of RNA Biology, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Xiaochang Yin
- State Key Laboratory of Protein and Plant Gene Research, School of Advanced Agricultural Sciences, Peking University, Beijing 100871, China
| | - Jia Shu
- State Key Laboratory of Protein and Plant Gene Research, School of Advanced Agricultural Sciences, Peking University, Beijing 100871, China
| | - Xing Dai
- Hunan Provincial Key Laboratory of Phytohormones and Growth Development, Hunan Agricultural University, Changsha 410128, China
| | - Yannan Liu
- State Key Laboratory of Protein and Plant Gene Research, School of Advanced Agricultural Sciences, Peking University, Beijing 100871, China
| | - Linhua Sun
- State Key Laboratory of Protein and Plant Gene Research, School of Advanced Agricultural Sciences, Peking University, Beijing 100871, China
- Peking University Institute of Advanced Agricultural Sciences, Weifang, Shandong 261325, China
| | - Danmeng Zhu
- State Key Laboratory of Protein and Plant Gene Research, School of Advanced Agricultural Sciences, Peking University, Beijing 100871, China
| | - Xing Wang Deng
- State Key Laboratory of Protein and Plant Gene Research, School of Advanced Agricultural Sciences, Peking University, Beijing 100871, China
- Peking University Institute of Advanced Agricultural Sciences, Weifang, Shandong 261325, China
| | - Keqiong Ye
- Key Laboratory of RNA Biology, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Weiqiang Qian
- State Key Laboratory of Protein and Plant Gene Research, School of Advanced Agricultural Sciences, Peking University, Beijing 100871, China
- Peking University Institute of Advanced Agricultural Sciences, Weifang, Shandong 261325, China
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6
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Hansen SR, White DS, Scalf M, Corrêa IR, Smith LM, Hoskins AA. Multi-step recognition of potential 5' splice sites by the Saccharomyces cerevisiae U1 snRNP. eLife 2022; 11:70534. [PMID: 35959885 PMCID: PMC9436412 DOI: 10.7554/elife.70534] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2021] [Accepted: 08/11/2022] [Indexed: 11/13/2022] Open
Abstract
In eukaryotes, splice sites define the introns of pre-mRNAs and must be recognized and excised with nucleotide precision by the spliceosome to make the correct mRNA product. In one of the earliest steps of spliceosome assembly, the U1 small nuclear ribonucleoprotein (snRNP) recognizes the 5' splice site (5' SS) through a combination of base pairing, protein-RNA contacts, and interactions with other splicing factors. Previous studies investigating the mechanisms of 5' SS recognition have largely been done in vivo or in cellular extracts where the U1/5' SS interaction is difficult to deconvolute from the effects of trans-acting factors or RNA structure. In this work we used colocalization single-molecule spectroscopy (CoSMoS) to elucidate the pathway of 5' SS selection by purified yeast U1 snRNP. We determined that U1 reversibly selects 5' SS in a sequence-dependent, two-step mechanism. A kinetic selection scheme enforces pairing at particular positions rather than overall duplex stability to achieve long-lived U1 binding. Our results provide a kinetic basis for how U1 may rapidly surveil nascent transcripts for 5' SS and preferentially accumulate at these sequences rather than on close cognates.
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Affiliation(s)
- Sarah R Hansen
- Department of Biochemistry, University of Wisconsin-Madison, Madison, United States
| | - David S White
- Department of Biochemistry, University of Wisconsin-Madison, Madison, United States
| | - Mark Scalf
- Department of Chemistry, University of Wisconsin-Madison, Madison, United States
| | | | - Lloyd M Smith
- Department of Chemistry, University of Wisconsin-Madison, Madison, United States
| | - Aaron A Hoskins
- Department of Biochemistry, University of Wisconsin-Madison, Madison, United States
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7
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Mabin JW, Lewis PW, Brow DA, Dvinge H. Human spliceosomal snRNA sequence variants generate variant spliceosomes. RNA (NEW YORK, N.Y.) 2021; 27:1186-1203. [PMID: 34234030 PMCID: PMC8457000 DOI: 10.1261/rna.078768.121] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/27/2021] [Accepted: 06/29/2021] [Indexed: 06/02/2023]
Abstract
Human pre-mRNA splicing is primarily catalyzed by the major spliceosome, comprising five small nuclear ribonucleoprotein complexes, U1, U2, U4, U5, and U6 snRNPs, each of which contains the corresponding U-rich snRNA. These snRNAs are encoded by large gene families exhibiting significant sequence variation, but it remains unknown if most human snRNA genes are untranscribed pseudogenes or produce variant snRNAs with the potential to differentially influence splicing. Since gene duplication and variation are powerful mechanisms of evolutionary adaptation, we sought to address this knowledge gap by systematically profiling human U1, U2, U4, and U5 snRNA variant gene transcripts. We identified 55 transcripts that are detectably expressed in human cells, 38 of which incorporate into snRNPs and spliceosomes in 293T cells. All U1 snRNA variants are more than 1000-fold less abundant in spliceosomes than the canonical U1, whereas at least 1% of spliceosomes contain a variant of U2 or U4. In contrast, eight U5 snRNA sequence variants occupy spliceosomes at levels of 1% to 46%. Furthermore, snRNA variants display distinct expression patterns across five human cell lines and adult and fetal tissues. Different RNA degradation rates contribute to the diverse steady state levels of snRNA variants. Our findings suggest that variant spliceosomes containing noncanonical snRNAs may contribute to different tissue- and cell-type-specific alternative splicing patterns.
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Affiliation(s)
- Justin W Mabin
- Department of Biomolecular Chemistry, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53706, USA
| | - Peter W Lewis
- Department of Biomolecular Chemistry, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53706, USA
| | - David A Brow
- Department of Biomolecular Chemistry, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53706, USA
| | - Heidi Dvinge
- Department of Biomolecular Chemistry, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53706, USA
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8
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Artemyeva-Isman OV, Porter ACG. U5 snRNA Interactions With Exons Ensure Splicing Precision. Front Genet 2021; 12:676971. [PMID: 34276781 PMCID: PMC8283771 DOI: 10.3389/fgene.2021.676971] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2021] [Accepted: 05/12/2021] [Indexed: 11/13/2022] Open
Abstract
Imperfect conservation of human pre-mRNA splice sites is necessary to produce alternative isoforms. This flexibility is combined with the precision of the message reading frame. Apart from intron-termini GU_AG and the branchpoint A, the most conserved are the exon-end guanine and +5G of the intron start. Association between these guanines cannot be explained solely by base-pairing with U1 snRNA in the early spliceosome complex. U6 succeeds U1 and pairs +5G in the pre-catalytic spliceosome, while U5 binds the exon end. Current U5 snRNA reconstructions by CryoEM cannot explain the conservation of the exon-end G. Conversely, human mutation analyses show that guanines of both exon termini can suppress splicing mutations. Our U5 hypothesis explains the mechanism of splicing precision and the role of these conserved guanines in the pre-catalytic spliceosome. We propose: (1) optimal binding register for human exons and U5-the exon junction positioned at U5Loop1 C39|C38; (2) common mechanism for base-pairing of human U5 snRNA with diverse exons and bacterial Ll.LtrB intron with new loci in retrotransposition-guided by base pair geometry; and (3) U5 plays a significant role in specific exon recognition in the pre-catalytic spliceosome. Statistical analyses showed increased U5 Watson-Crick pairs with the 5'exon in the absence of +5G at the intron start. In 5'exon positions -3 and -5, this effect is specific to U5 snRNA rather than U1 snRNA of the early spliceosome. Increased U5 Watson-Crick pairs with 3'exon position +1 coincide with substitutions of the conserved -3C at the intron 3'end. Based on mutation and X-ray evidence, we propose that -3C pairs with U2 G31 juxtaposing the branchpoint and the 3'intron end. The intron-termini pair, formed in the pre-catalytic spliceosome to be ready for transition after branching, and the early involvement of the 3'intron end ensure that the 3'exon contacts U5 in the pre-catalytic complex. We suggest that splicing precision is safeguarded cooperatively by U5, U6, and U2 snRNAs that stabilize the pre-catalytic complex by Watson-Crick base pairing. In addition, our new U5 model explains the splicing effect of exon-start +1G mutations: U5 Watson-Crick pairs with exon +2C/+3G strongly promote exon inclusion. We discuss potential applications for snRNA therapeutics and gene repair by reverse splicing.
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Affiliation(s)
- Olga V Artemyeva-Isman
- Gene Targeting Group, Centre for Haematology, Department of Immunology and Inflammation, Faculty of Medicine, Imperial College London, London, United Kingdom
| | - Andrew C G Porter
- Gene Targeting Group, Centre for Haematology, Department of Immunology and Inflammation, Faculty of Medicine, Imperial College London, London, United Kingdom
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9
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A single m 6A modification in U6 snRNA diversifies exon sequence at the 5' splice site. Nat Commun 2021; 12:3244. [PMID: 34050143 PMCID: PMC8163875 DOI: 10.1038/s41467-021-23457-6] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2019] [Accepted: 04/29/2021] [Indexed: 11/09/2022] Open
Abstract
N6-methyladenosine (m6A) is a modification that plays pivotal roles in RNA metabolism and function, although its functions in spliceosomal U6 snRNA remain unknown. To elucidate its role, we conduct a large-scale transcriptome analysis of a Schizosaccharomyces pombe strain lacking this modification and found a global change of pre-mRNA splicing. The most significantly impacted introns are enriched for adenosine at the fourth position pairing the m6A in U6 snRNA, and exon sequences weakly recognized by U5 snRNA. This suggests cooperative recognition of 5' splice site by U6 and U5 snRNPs, and also a role of m6A facilitating efficient recognition of the splice sites weakly interacting with U5 snRNA, indicating that U6 snRNA m6A relaxes the 5' exon constraint and allows protein sequence diversity along with explosively increasing number of introns over the course of eukaryotic evolution.
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10
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Joseph B, Lai EC. The Exon Junction Complex and intron removal prevent re-splicing of mRNA. PLoS Genet 2021; 17:e1009563. [PMID: 34033644 PMCID: PMC8184009 DOI: 10.1371/journal.pgen.1009563] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2020] [Revised: 06/07/2021] [Accepted: 04/26/2021] [Indexed: 01/23/2023] Open
Abstract
Accurate splice site selection is critical for fruitful gene expression. Recently, the mammalian EJC was shown to repress competing, cryptic, splice sites (SS). However, the evolutionary generality of this remains unclear. Here, we demonstrate the Drosophila EJC suppresses hundreds of functional cryptic SS, even though most bear weak splicing motifs and are seemingly incompetent. Mechanistically, the EJC directly conceals cryptic splicing elements by virtue of its position-specific recruitment, preventing aberrant SS definition. Unexpectedly, we discover the EJC inhibits scores of regenerated 5' and 3' recursive SS on segments that have already undergone splicing, and that loss of EJC regulation triggers faulty resplicing of mRNA. An important corollary is that certain intronless cDNA constructs yield unanticipated, truncated transcripts generated by resplicing. We conclude the EJC has conserved roles to defend transcriptome fidelity by (1) repressing illegitimate splice sites on pre-mRNAs, and (2) preventing inadvertent activation of such sites on spliced segments.
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Affiliation(s)
- Brian Joseph
- Developmental Biology Program, Sloan Kettering Institute, New York, New York, United States of America
- Louis V. Gerstner, Jr. Graduate School of Biomedical Sciences, Memorial Sloan Kettering Cancer Center, New York, New York, United States of America
| | - Eric C. Lai
- Developmental Biology Program, Sloan Kettering Institute, New York, New York, United States of America
- Louis V. Gerstner, Jr. Graduate School of Biomedical Sciences, Memorial Sloan Kettering Cancer Center, New York, New York, United States of America
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11
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Wilkinson ME, Fica SM, Galej WP, Nagai K. Structural basis for conformational equilibrium of the catalytic spliceosome. Mol Cell 2021; 81:1439-1452.e9. [PMID: 33705709 PMCID: PMC8022279 DOI: 10.1016/j.molcel.2021.02.021] [Citation(s) in RCA: 28] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2020] [Revised: 12/14/2020] [Accepted: 02/11/2021] [Indexed: 12/21/2022]
Abstract
The ATPase Prp16 governs equilibrium between the branching (B∗/C) and exon ligation (C∗/P) conformations of the spliceosome. Here, we present the electron cryomicroscopy reconstruction of the Saccharomyces cerevisiae C-complex spliceosome at 2.8 Å resolution and identify a novel C-complex intermediate (Ci) that elucidates the molecular basis for this equilibrium. The exon-ligation factors Prp18 and Slu7 bind to Ci before ATP hydrolysis by Prp16 can destabilize the branching conformation. Biochemical assays suggest that these pre-bound factors prime the C complex for conversion to C∗ by Prp16. A complete model of the Prp19 complex (NTC) reveals how the branching factors Yju2 and Isy1 are recruited by the NTC before branching. Prp16 remodels Yju2 binding after branching, allowing Yju2 to remain tethered to the NTC in the C∗ complex to promote exon ligation. Our results explain how Prp16 action modulates the dynamic binding of step-specific factors to alternatively stabilize the C or C∗ conformation and establish equilibrium of the catalytic spliceosome. Cryo-EM reveals new Ci spliceosome intermediate between branching and exon ligation Binding of branching and exon-ligation factors to Ci governs spliceosome equilibrium Exon-ligation factors Slu7 and Prp18 bind Ci weakly before Prp16 action After Prp16 action, pre-bound Slu7 and Prp18 bind strongly to promote exon ligation
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Affiliation(s)
- Max E Wilkinson
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge Biomedical Campus, Cambridge CB2 0QH, UK.
| | - Sebastian M Fica
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge Biomedical Campus, Cambridge CB2 0QH, UK.
| | - Wojciech P Galej
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge Biomedical Campus, Cambridge CB2 0QH, UK
| | - Kiyoshi Nagai
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge Biomedical Campus, Cambridge CB2 0QH, UK
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12
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Morais P, Adachi H, Yu YT. Spliceosomal snRNA Epitranscriptomics. Front Genet 2021; 12:652129. [PMID: 33737950 PMCID: PMC7960923 DOI: 10.3389/fgene.2021.652129] [Citation(s) in RCA: 43] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2021] [Accepted: 02/08/2021] [Indexed: 12/15/2022] Open
Abstract
Small nuclear RNAs (snRNAs) are critical components of the spliceosome that catalyze the splicing of pre-mRNA. snRNAs are each complexed with many proteins to form RNA-protein complexes, termed as small nuclear ribonucleoproteins (snRNPs), in the cell nucleus. snRNPs participate in pre-mRNA splicing by recognizing the critical sequence elements present in the introns, thereby forming active spliceosomes. The recognition is achieved primarily by base-pairing interactions (or nucleotide-nucleotide contact) between snRNAs and pre-mRNA. Notably, snRNAs are extensively modified with different RNA modifications, which confer unique properties to the RNAs. Here, we review the current knowledge of the mechanisms and functions of snRNA modifications and their biological relevance in the splicing process.
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Affiliation(s)
| | - Hironori Adachi
- Department of Biochemistry and Biophysics, Center for RNA Biology, University of Rochester Medical Center, Rochester, NY, United States
| | - Yi-Tao Yu
- Department of Biochemistry and Biophysics, Center for RNA Biology, University of Rochester Medical Center, Rochester, NY, United States
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13
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Wood KA, Eadsforth MA, Newman WG, O'Keefe RT. The Role of the U5 snRNP in Genetic Disorders and Cancer. Front Genet 2021; 12:636620. [PMID: 33584830 PMCID: PMC7876476 DOI: 10.3389/fgene.2021.636620] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2020] [Accepted: 01/04/2021] [Indexed: 12/14/2022] Open
Abstract
Pre-mRNA splicing is performed by the spliceosome, a dynamic macromolecular complex consisting of five small uridine-rich ribonucleoprotein complexes (the U1, U2, U4, U5, and U6 snRNPs) and numerous auxiliary splicing factors. A plethora of human disorders are caused by genetic variants affecting the function and/or expression of splicing factors, including the core snRNP proteins. Variants in the genes encoding proteins of the U5 snRNP cause two distinct and tissue-specific human disease phenotypes – variants in PRPF6, PRPF8, and SNRP200 are associated with retinitis pigmentosa (RP), while variants in EFTUD2 and TXNL4A cause the craniofacial disorders mandibulofacial dysostosis Guion-Almeida type (MFDGA) and Burn-McKeown syndrome (BMKS), respectively. Furthermore, recurrent somatic mutations or changes in the expression levels of a number of U5 snRNP proteins (PRPF6, PRPF8, EFTUD2, DDX23, and SNRNP40) have been associated with human cancers. How and why variants in ubiquitously expressed spliceosome proteins required for pre-mRNA splicing in all human cells result in tissue-restricted disease phenotypes is not clear. Additionally, why variants in different, yet interacting, proteins making up the same core spliceosome snRNP result in completely distinct disease outcomes – RP, craniofacial defects or cancer – is unclear. In this review, we define the roles of different U5 snRNP proteins in RP, craniofacial disorders and cancer, including how disease-associated genetic variants affect pre-mRNA splicing and the proposed disease mechanisms. We then propose potential hypotheses for how U5 snRNP variants cause tissue specificity resulting in the restricted and distinct human disorders.
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Affiliation(s)
- Katherine A Wood
- Division of Evolution and Genomic Sciences, Faculty of Biology, Medicine and Health, School of Biological Sciences, The University of Manchester, Manchester, United Kingdom.,Manchester Centre for Genomic Medicine, Manchester Academic Health Science Centre, Manchester University NHS Foundation Trust, Manchester, United Kingdom
| | - Megan A Eadsforth
- Division of Evolution and Genomic Sciences, Faculty of Biology, Medicine and Health, School of Biological Sciences, The University of Manchester, Manchester, United Kingdom
| | - William G Newman
- Division of Evolution and Genomic Sciences, Faculty of Biology, Medicine and Health, School of Biological Sciences, The University of Manchester, Manchester, United Kingdom.,Manchester Centre for Genomic Medicine, Manchester Academic Health Science Centre, Manchester University NHS Foundation Trust, Manchester, United Kingdom
| | - Raymond T O'Keefe
- Division of Evolution and Genomic Sciences, Faculty of Biology, Medicine and Health, School of Biological Sciences, The University of Manchester, Manchester, United Kingdom
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14
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Larsen NA. The SF3b Complex is an Integral Component of the Spliceosome and Targeted by Natural Product-Based Inhibitors. Subcell Biochem 2021; 96:409-432. [PMID: 33252738 DOI: 10.1007/978-3-030-58971-4_12] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
Abstract
In this chapter, the essential role of the SF3b multi-protein complex will be discussed in the context of the overall spliceosome. SF3b is critical during spliceosome assembly for recognition of the branch point (BP) adenosine and, by de facto, selection of the 3' splice site. This complex is highly dynamic, undergoing significant conformational changes upon loading of the branch duplex RNA and in its relative positioning during spliceosomal remodeling from the A, pre-B, B, Bact and B* complexes. Ultimately, during the spliceosome activation phase, SF3b must be displaced to unmask the branch point adenosine for the first splicing reaction to occur. In certain cancers, such as the hematological malignancies CML, CLL and MDS, the SF3b subunit SF3B1 is frequently mutated. Recent studies suggest these mutations lead to inappropriate branch point selection and mis-splicing events that appear to be drivers of disease. Finally, the SF3b complex is the target for at least three different classes of natural product-based inhibitors. These inhibitors bind in the BP adenosine-binding pocket and demonstrate a pre-mRNA competitive mechanism of action resulting in either intron retention or exon skipping. These compounds are extremely useful as chemical probes to isolate and characterize early stages of spliceosome assembly. They are also being explored preclinically and clinically as possible agents for hematological cancers.
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15
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Abstract
Splicing of the precursor messenger RNA, involving intron removal and exon ligation, is mediated by the spliceosome. Together with biochemical and genetic investigations of the past four decades, structural studies of the intact spliceosome at atomic resolution since 2015 have led to mechanistic delineation of RNA splicing with remarkable insights. The spliceosome is proven to be a protein-orchestrated metalloribozyme. Conserved elements of small nuclear RNA (snRNA) constitute the splicing active site with two catalytic metal ions and recognize three conserved intron elements through duplex formation, which are delivered into the splicing active site for branching and exon ligation. The protein components of the spliceosome stabilize the conformation of the snRNA, drive spliceosome remodeling, orchestrate the movement of the RNA elements, and facilitate the splicing reaction. The overall organization of the spliceosome and the configuration of the splicing active site are strictly conserved between human and yeast.
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Affiliation(s)
- Ruixue Wan
- Beijing Advanced Innovation Center for Structural Biology, School of Life Sciences and School of Medicine, Tsinghua University, Beijing 100084, China;,
| | - Rui Bai
- Institute of Biology, Westlake Institute for Advanced Study, Westlake University, Hangzhou 310024, China
| | - Xiechao Zhan
- Beijing Advanced Innovation Center for Structural Biology, School of Life Sciences and School of Medicine, Tsinghua University, Beijing 100084, China;,
| | - Yigong Shi
- Beijing Advanced Innovation Center for Structural Biology, School of Life Sciences and School of Medicine, Tsinghua University, Beijing 100084, China;,
- Institute of Biology, Westlake Institute for Advanced Study, Westlake University, Hangzhou 310024, China
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16
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Abstract
The spliceosome removes introns from messenger RNA precursors (pre-mRNA). Decades of biochemistry and genetics combined with recent structural studies of the spliceosome have produced a detailed view of the mechanism of splicing. In this review, we aim to make this mechanism understandable and provide several videos of the spliceosome in action to illustrate the intricate choreography of splicing. The U1 and U2 small nuclear ribonucleoproteins (snRNPs) mark an intron and recruit the U4/U6.U5 tri-snRNP. Transfer of the 5' splice site (5'SS) from U1 to U6 snRNA triggers unwinding of U6 snRNA from U4 snRNA. U6 folds with U2 snRNA into an RNA-based active site that positions the 5'SS at two catalytic metal ions. The branch point (BP) adenosine attacks the 5'SS, producing a free 5' exon. Removal of the BP adenosine from the active site allows the 3'SS to bind, so that the 5' exon attacks the 3'SS to produce mature mRNA and an excised lariat intron.
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Affiliation(s)
- Max E Wilkinson
- MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom; ,
| | - Clément Charenton
- MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom; ,
| | - Kiyoshi Nagai
- MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom; ,
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17
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Kastner B, Will CL, Stark H, Lührmann R. Structural Insights into Nuclear pre-mRNA Splicing in Higher Eukaryotes. Cold Spring Harb Perspect Biol 2019; 11:cshperspect.a032417. [PMID: 30765414 DOI: 10.1101/cshperspect.a032417] [Citation(s) in RCA: 116] [Impact Index Per Article: 23.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The spliceosome is a highly complex, dynamic ribonucleoprotein molecular machine that undergoes numerous structural and compositional rearrangements that lead to the formation of its active site. Recent advances in cyroelectron microscopy (cryo-EM) have provided a plethora of near-atomic structural information about the inner workings of the spliceosome. Aided by previous biochemical, structural, and functional studies, cryo-EM has confirmed or provided a structural basis for most of the prevailing models of spliceosome function, but at the same time allowed novel insights into splicing catalysis and the intriguing dynamics of the spliceosome. The mechanism of pre-mRNA splicing is highly conserved between humans and yeast, but the compositional dynamics and ribonucleoprotein (RNP) remodeling of the human spliceosome are more complex. Here, we summarize recent advances in our understanding of the molecular architecture of the human spliceosome, highlighting differences between the human and yeast splicing machineries.
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Affiliation(s)
- Berthold Kastner
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, D-37077 Göttingen, Germany
| | - Cindy L Will
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, D-37077 Göttingen, Germany
| | - Holger Stark
- Department of Structural Dynamics, Max Planck Institute for Biophysical Chemistry, D-37077 Göttingen, Germany
| | - Reinhard Lührmann
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, D-37077 Göttingen, Germany
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18
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Smathers CM, Robart AR. The mechanism of splicing as told by group II introns: Ancestors of the spliceosome. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2019; 1862:194390. [PMID: 31202783 DOI: 10.1016/j.bbagrm.2019.06.001] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Accepted: 06/10/2019] [Indexed: 12/31/2022]
Abstract
Spliceosomal introns and self-splicing group II introns share a common mechanism of intron splicing where two sequential transesterification reactions remove intron lariats and ligate exons. The recent revolution in cryo-electron microscopy (cryo-EM) has allowed visualization of the spliceosome's ribozyme core. Comparison of these cryo-EM structures to recent group II intron crystal structures presents an opportunity to draw parallels between the RNA active site, substrate positioning, and product formation in these two model systems of intron splicing. In addition to shared RNA architectural features, structural similarity between group II intron encoded proteins (IEPs) and the integral spliceosomal protein Prp8 further support a shared catalytic core. These mechanistic and structural similarities support the long-held assertion that group II introns and the eukaryotic spliceosome have a common evolutionary origin. In this review, we discuss how recent structural insights into group II introns and the spliceosome facilitate the chemistry of splicing, highlight similarities between the two systems, and discuss their likely evolutionary connections. This article is part of a Special Issue entitled: RNA structure and splicing regulation edited by Francisco Baralle, Ravindra Singh and Stefan Stamm.
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Affiliation(s)
- Claire M Smathers
- Department of Biochemistry, West Virginia University, Morgantown, WV, United States of America
| | - Aaron R Robart
- Department of Biochemistry, West Virginia University, Morgantown, WV, United States of America.
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19
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Plaschka C, Newman AJ, Nagai K. Structural Basis of Nuclear pre-mRNA Splicing: Lessons from Yeast. Cold Spring Harb Perspect Biol 2019; 11:cshperspect.a032391. [PMID: 30765413 DOI: 10.1101/cshperspect.a032391] [Citation(s) in RCA: 53] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Noncoding introns are removed from nuclear precursor messenger RNA (pre-mRNA) in a two-step phosphoryl transfer reaction by the spliceosome, a dynamic multimegadalton enzyme. Cryo-electron microscopy (cryo-EM) structures of the Saccharomyces cerevisiae spliceosome were recently determined in eight key states. Combined with the wealth of available genetic and biochemical data, these structures have revealed new insights into the mechanisms of spliceosome assembly, activation, catalysis, and disassembly. The structures show how a single RNA catalytic center forms during activation and accomplishes both steps of the splicing reaction. The structures reveal how spliceosomal helicases remodel the spliceosome for active site formation, substrate docking, reaction product undocking, and spliceosome disassembly and how they facilitate splice site proofreading. Although human spliceosomes contain additional proteins, their cryo-EM structures suggest that the underlying mechanism is conserved across all eukaryotes. In this review, we summarize the current structural understanding of pre-mRNA splicing.
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Affiliation(s)
- Clemens Plaschka
- MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom
| | - Andrew J Newman
- 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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20
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Åsman AKM, Curtis BA, Archibald JM. Nucleomorph Small RNAs in Cryptophyte and Chlorarachniophyte Algae. Genome Biol Evol 2019; 11:1117-1134. [PMID: 30949682 PMCID: PMC6461891 DOI: 10.1093/gbe/evz064] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/15/2019] [Indexed: 12/27/2022] Open
Abstract
The regulation of gene expression and RNA maturation underlies fundamental processes such as cell homeostasis, development, and stress acclimation. The biogenesis and modification of RNA is tightly controlled by an array of regulatory RNAs and nucleic acid-binding proteins. While the role of small RNAs (sRNAs) in gene expression has been studied in-depth in select model organisms, little is known about sRNA biology across the eukaryotic tree of life. We used deep sequencing to explore the repertoires of sRNAs encoded by the miniaturized, endosymbiotically derived “nucleomorph” genomes of two single-celled algae, the cryptophyte Guillardia theta and the chlorarachniophyte Bigelowiella natans. A total of 32.3 and 35.3 million reads were generated from G. theta and B. natans, respectively. In G. theta, we identified nucleomorph U1, U2, and U4 spliceosomal small nuclear RNAs (snRNAs) as well as 11 C/D box small nucleolar RNAs (snoRNAs), five of which have potential plant and animal homologs. The snoRNAs are predicted to perform 2′-O methylation of rRNA (but not snRNA). In B. natans, we found the previously undetected 5S rRNA as well as six orphan sRNAs. Analysis of chlorarachniophyte snRNAs shed light on the removal of the miniature 18–21 nt introns found in B. natans nucleomorph genes. Neither of the nucleomorph genomes appears to encode RNA pseudouridylation machinery, and U5 snRNA cannot be found in the cryptophyte G. theta. Considering the central roles of U5 snRNA and RNA modifications in other organisms, cytoplasm-to-nucleomorph RNA shuttling in cryptophyte algae is a distinct possibility.
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Affiliation(s)
- Anna K M Åsman
- Department of Biochemistry and Molecular Biology, Dalhousie University, Nova Scotia, Canada.,Department of Molecular Sciences, Uppsala BioCenter, Swedish University of Agricultural Sciences and Linnean Center for Plant Biology, Uppsala, Sweden
| | - Bruce A Curtis
- Department of Biochemistry and Molecular Biology, Dalhousie University, Nova Scotia, Canada
| | - John M Archibald
- Department of Biochemistry and Molecular Biology, Dalhousie University, Nova Scotia, Canada
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21
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Xia X. RNA-Seq approach for accurate characterization of splicing efficiency of yeast introns. Methods 2019; 176:25-33. [PMID: 30926533 DOI: 10.1016/j.ymeth.2019.03.019] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2018] [Revised: 03/12/2019] [Accepted: 03/19/2019] [Indexed: 01/21/2023] Open
Abstract
Introns in different genes, or even different introns within the same gene, often have different splice sites and differ in splicing efficiency (SE). One expects mass-transcribed genes to have introns with higher SE than weakly transcribed genes. However, such a simple expectation cannot be tested directly because variable SE for these genes is often not measured. Mechanistically, SE should depend on signal strength at key splice sites (SS) such as 5'SS, 3'SS and branchpoint site (BPS), i.e., SE = F(5'SS, 3'SS, BPS). However, without SE, we again cannot model how these splice sites contribute to SE. Here I present an RNA-Seq approach to quantify SE for each of the 304 introns in yeast (Saccharomyces cerevisiae) genes, including 24 in the 5'UTR, by measuring 1) number of reads mapped to exon-exon junctions (NEE) as a proxy for the abundance of spliced form, and 2) number of reads mapped to exon-intron junction (NEI5 and NEI3 at 5' and 3' ends of intron) as a proxy for the abundance of unspliced form. The total mRNA is NTotal = NEE + p * NEI5 + (1-p) * NEI3, with the simplest p = 0.5 but statistical methods were presented to estimate p from data. An estimated p is needed because NEI5 is expected to be smaller than NEI3 due to 1) step 1 splicing occurs before step 2 so EI5 is broken before EI3, 2) enrichment of poly(A) mRNA by oligo-dT, and 3) 5' degradation. SE is defined as the proportion (NEE/NTotal). Application of the method shows that ribosomal protein messages are efficiently and mostly cotranscriptionally spliced. Yeast genes with long introns are also spliced efficiently. HAC1/YFL031W is poorly spliced partly because its splicing involves a nonspliceosome mechanism and partly because Ire1p, which participate in splicing HAC1, is hardly expressed. Many putative yeast genes have low SE, and some splice sites are incorrectly annotated.
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Affiliation(s)
- Xuhua Xia
- Department of Biology, University of Ottawa, 30 Marie Curie, Ottawa K1N 6N5, Canada; Ottawa Institute of Systems Biology, Ottawa, Ontario K1H 8M5, Canada.
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22
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Fica SM, Oubridge C, Wilkinson ME, Newman AJ, Nagai K. A human postcatalytic spliceosome structure reveals essential roles of metazoan factors for exon ligation. Science 2019; 363:710-714. [PMID: 30705154 DOI: 10.1126/science.aaw5569] [Citation(s) in RCA: 66] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2019] [Accepted: 01/21/2019] [Indexed: 12/11/2022]
Abstract
During exon ligation, the Saccharomyces cerevisiae spliceosome recognizes the 3'-splice site (3'SS) of precursor messenger RNA (pre-mRNA) through non-Watson-Crick pairing with the 5'SS and the branch adenosine, in a conformation stabilized by Prp18 and Prp8. Here we present the 3.3-angstrom cryo-electron microscopy structure of a human postcatalytic spliceosome just after exon ligation. The 3'SS docks at the active site through conserved RNA interactions in the absence of Prp18. Unexpectedly, the metazoan-specific FAM32A directly bridges the 5'-exon and intron 3'SS of pre-mRNA and promotes exon ligation, as shown by functional assays. CACTIN, SDE2, and NKAP-factors implicated in alternative splicing-further stabilize the catalytic conformation of the spliceosome during exon ligation. Together these four proteins act as exon ligation factors. Our study reveals how the human spliceosome has co-opted additional proteins to modulate a conserved RNA-based mechanism for 3'SS selection and to potentially fine-tune alternative splicing at the exon ligation stage.
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Affiliation(s)
- Sebastian M Fica
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK.
| | - Chris Oubridge
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
| | - Max E Wilkinson
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
| | - Andrew J Newman
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
| | - Kiyoshi Nagai
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK.
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23
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Zhan X, Yan C, Zhang X, Lei J, Shi Y. Structures of the human pre-catalytic spliceosome and its precursor spliceosome. Cell Res 2018; 28:1129-1140. [PMID: 30315277 PMCID: PMC6274647 DOI: 10.1038/s41422-018-0094-7] [Citation(s) in RCA: 70] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2018] [Revised: 09/05/2018] [Accepted: 09/06/2018] [Indexed: 12/13/2022] Open
Abstract
The pre-catalytic spliceosome (B complex) is preceded by its precursor spliceosome (pre-B complex) and followed by the activated spliceosome (Bact complex). The pre-B-to-B and B-to-Bact transitions are driven by the ATPase/helicases Prp28 and Brr2, respectively. In this study, we report the cryo-electron microscopy structures of the human pre-B complex and the human B complex at an average resolution of 5.7 and 3.8 Å, respectively. In the pre-B complex, U1 and U2 small nuclear ribonucleoproteins (snRNPs) associate with two edges of the tetrahedron-shaped U4/U6.U5 tri-snRNP. The pre-mRNA is yet to be recognized by U5 or U6 small nuclear RNA (snRNA), and loop I of U5 snRNA remains unengaged. In the B complex, U1 snRNP and Prp28 are dissociated, the 5'-exon is anchored to loop I of U5 snRNA, and the 5'-splice site is recognized by U6 snRNA through duplex formation. In sharp contrast to S. cerevisiae, most components of U2 snRNP and tri-snRNP, exemplified by Brr2, undergo pronounced rearrangements in the human pre-B-to-B transition. Structural analysis reveals mechanistic insights into the assembly and activation of the human spliceosome.
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Affiliation(s)
- Xiechao Zhan
- Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences and School of Medicine, Tsinghua University, Beijing, 100084, China
| | - Chuangye Yan
- Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences and School of Medicine, Tsinghua University, Beijing, 100084, China.
| | - Xiaofeng Zhang
- Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences and School of Medicine, Tsinghua University, Beijing, 100084, China
| | - Jianlin Lei
- Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences and School of Medicine, Tsinghua University, Beijing, 100084, China
- Technology Center for Protein Sciences, Ministry of Education Key Laboratory of Protein Sciences, School of Life Sciences, Tsinghua University, Beijing, 100084, China
| | - Yigong Shi
- Beijing Advanced Innovation Center for Structural Biology, Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences and School of Medicine, Tsinghua University, Beijing, 100084, China.
- Institute of Biology, Westlake Institute for Advanced Study, Westlake University, 18 Shilongshan Road, Xihu District, Hangzhou, Zhejiang, 310024, China.
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24
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Structural studies of the spliceosome: past, present and future perspectives. Biochem Soc Trans 2018; 46:1407-1422. [PMID: 30420411 DOI: 10.1042/bst20170240] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2018] [Revised: 09/24/2018] [Accepted: 09/25/2018] [Indexed: 12/18/2022]
Abstract
The spliceosome is a multi-subunit RNA-protein complex involved in the removal of non-coding segments (introns) from between the coding regions (exons) in precursors of messenger RNAs (pre-mRNAs). Intron removal proceeds via two transesterification reactions, occurring between conserved sequences at intron-exon junctions. A tightly regulated, hierarchical assembly with a multitude of structural and compositional rearrangements posed a great challenge for structural studies of the spliceosome. Over the years, X-ray crystallography dominated the field, providing valuable high-resolution structural information that was mostly limited to individual proteins and smaller sub-complexes. Recent developments in the field of cryo-electron microscopy allowed the visualisation of fully assembled yeast and human spliceosomes, providing unprecedented insights into substrate recognition, catalysis, and active site formation. This has advanced our mechanistic understanding of pre-mRNA splicing enormously.
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25
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Wong MS, Kinney JB, Krainer AR. Quantitative Activity Profile and Context Dependence of All Human 5' Splice Sites. Mol Cell 2018; 71:1012-1026.e3. [PMID: 30174293 DOI: 10.1016/j.molcel.2018.07.033] [Citation(s) in RCA: 55] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2018] [Revised: 06/18/2018] [Accepted: 07/23/2018] [Indexed: 02/02/2023]
Abstract
Pre-mRNA splicing is an essential step in the expression of most human genes. Mutations at the 5' splice site (5'ss) frequently cause defective splicing and disease due to interference with the initial recognition of the exon-intron boundary by U1 small nuclear ribonucleoprotein (snRNP), a component of the spliceosome. Here, we use a massively parallel splicing assay (MPSA) in human cells to quantify the activity of all 32,768 unique 5'ss sequences (NNN/GYNNNN) in three different gene contexts. Our results reveal that although splicing efficiency is mostly governed by the 5'ss sequence, there are substantial differences in this efficiency across gene contexts. Among other uses, these MPSA measurements facilitate the prediction of 5'ss sequence variants that are likely to cause aberrant splicing. This approach provides a framework to assess potential pathogenic variants in the human genome and streamline the development of splicing-corrective therapies.
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Affiliation(s)
- Mandy S Wong
- Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA
| | - Justin B Kinney
- Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA.
| | - Adrian R Krainer
- Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA.
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26
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Didychuk AL, Butcher SE, Brow DA. The life of U6 small nuclear RNA, from cradle to grave. RNA (NEW YORK, N.Y.) 2018; 24:437-460. [PMID: 29367453 PMCID: PMC5855946 DOI: 10.1261/rna.065136.117] [Citation(s) in RCA: 67] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Removal of introns from precursor messenger RNA (pre-mRNA) and some noncoding transcripts is an essential step in eukaryotic gene expression. In the nucleus, this process of RNA splicing is carried out by the spliceosome, a multi-megaDalton macromolecular machine whose core components are conserved from yeast to humans. In addition to many proteins, the spliceosome contains five uridine-rich small nuclear RNAs (snRNAs) that undergo an elaborate series of conformational changes to correctly recognize the splice sites and catalyze intron removal. Decades of biochemical and genetic data, along with recent cryo-EM structures, unequivocally demonstrate that U6 snRNA forms much of the catalytic core of the spliceosome and is highly dynamic, interacting with three snRNAs, the pre-mRNA substrate, and >25 protein partners throughout the splicing cycle. This review summarizes the current state of knowledge on how U6 snRNA is synthesized, modified, incorporated into snRNPs and spliceosomes, recycled, and degraded.
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Affiliation(s)
- Allison L Didychuk
- Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA
| | - Samuel E Butcher
- Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA
| | - David A Brow
- Department of Biomolecular Chemistry, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin 53706, USA
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27
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Galej WP, Toor N, Newman AJ, Nagai K. Molecular Mechanism and Evolution of Nuclear Pre-mRNA and Group II Intron Splicing: Insights from Cryo-Electron Microscopy Structures. Chem Rev 2018; 118:4156-4176. [PMID: 29377672 DOI: 10.1021/acs.chemrev.7b00499] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Nuclear pre-mRNA splicing and group II intron self-splicing both proceed by two-step transesterification reactions via a lariat intron intermediate. Recently determined cryo-electron microscopy (cryo-EM) structures of catalytically active spliceosomes revealed the RNA-based catalytic core and showed how pre-mRNA substrates and reaction products are positioned in the active site. These findings highlight a strong structural similarity to the group II intron active site, strengthening the notion that group II introns and spliceosomes evolved from a common ancestor. Prp8, the largest and most conserved protein in the spliceosome, cradles the active site RNA. Prp8 and group II intron maturase have a similar domain architecture, suggesting that they also share a common evolutionary origin. The interactions between maturase and key group II intron RNA elements, such as the exon-binding loop and domains V and VI, are recapitulated in the interactions between Prp8 and key elements in the spliceosome's catalytic RNA core. Structural comparisons suggest that the extensive RNA scaffold of the group II intron was gradually replaced by proteins as the spliceosome evolved. A plausible model of spliceosome evolution is discussed.
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Affiliation(s)
- Wojciech P Galej
- EMBL Grenoble , 71 Avenue des Martyrs , 38042 Grenoble Cedex 09 , France
| | - Navtej Toor
- Department of Chemistry and Biochemistry , University of California, San Diego , La Jolla , California 92093 , United States
| | - Andrew J Newman
- MRC Laboratory of Molecular Biology , Francis Crick Avenue , Cambridge CB2 0QH , U.K
| | - Kiyoshi Nagai
- MRC Laboratory of Molecular Biology , Francis Crick Avenue , Cambridge CB2 0QH , U.K
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28
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Liu S, Li X, Zhang L, Jiang J, Hill RC, Cui Y, Hansen KC, Zhou ZH, Zhao R. Structure of the yeast spliceosomal postcatalytic P complex. Science 2017; 358:1278-1283. [PMID: 29146870 PMCID: PMC5828012 DOI: 10.1126/science.aar3462] [Citation(s) in RCA: 73] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2017] [Accepted: 11/09/2017] [Indexed: 12/20/2022]
Abstract
The spliceosome undergoes dramatic changes in a splicing cycle. Structures of B, Bact, C, C*, and intron lariat spliceosome complexes revealed mechanisms of 5'-splice site (ss) recognition, branching, and intron release, but lacked information on 3'-ss recognition, exon ligation, and exon release. Here we report a cryo-electron microscopy structure of the postcatalytic P complex at 3.3-angstrom resolution, revealing that the 3' ss is mainly recognized through non-Watson-Crick base pairing with the 5' ss and branch point. Furthermore, one or more unidentified proteins become stably associated with the P complex, securing the 3' exon and potentially regulating activity of the helicase Prp22. Prp22 binds nucleotides 15 to 21 in the 3' exon, enabling it to pull the intron-exon or ligated exons in a 3' to 5' direction to achieve 3'-ss proofreading or exon release, respectively.
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Affiliation(s)
- Shiheng Liu
- Electron Imaging Center for Nanomachines, University of California, Los Angeles (UCLA), Los Angeles, CA 90095, USA
- Department of Microbiology, Immunology, and Molecular Genetics, UCLA, Los Angeles, CA 90095, USA
| | - Xueni Li
- Department of Biochemistry and Molecular Genetics, University of Colorado Denver (UCD), Anschutz Medical Campus, Aurora, CO 80045, USA
| | - Lingdi Zhang
- Department of Biochemistry and Molecular Genetics, University of Colorado Denver (UCD), Anschutz Medical Campus, Aurora, CO 80045, USA
| | - Jiansen Jiang
- Electron Imaging Center for Nanomachines, University of California, Los Angeles (UCLA), Los Angeles, CA 90095, USA
- Department of Microbiology, Immunology, and Molecular Genetics, UCLA, Los Angeles, CA 90095, USA
| | - Ryan C Hill
- Department of Biochemistry and Molecular Genetics, University of Colorado Denver (UCD), Anschutz Medical Campus, Aurora, CO 80045, USA
| | - Yanxiang Cui
- Electron Imaging Center for Nanomachines, University of California, Los Angeles (UCLA), Los Angeles, CA 90095, USA
| | - Kirk C Hansen
- Department of Biochemistry and Molecular Genetics, University of Colorado Denver (UCD), Anschutz Medical Campus, Aurora, CO 80045, USA
| | - Z Hong Zhou
- Electron Imaging Center for Nanomachines, University of California, Los Angeles (UCLA), Los Angeles, CA 90095, USA.
- Department of Microbiology, Immunology, and Molecular Genetics, UCLA, Los Angeles, CA 90095, USA
| | - Rui Zhao
- Department of Biochemistry and Molecular Genetics, University of Colorado Denver (UCD), Anschutz Medical Campus, Aurora, CO 80045, USA.
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29
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Wilkinson ME, Fica SM, Galej WP, Norman CM, Newman AJ, Nagai K. Postcatalytic spliceosome structure reveals mechanism of 3'-splice site selection. Science 2017; 358:1283-1288. [PMID: 29146871 DOI: 10.1126/science.aar3729] [Citation(s) in RCA: 78] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2017] [Accepted: 11/09/2017] [Indexed: 12/27/2022]
Abstract
Introns are removed from eukaryotic messenger RNA precursors by the spliceosome in two transesterification reactions-branching and exon ligation. The mechanism of 3'-splice site recognition during exon ligation has remained unclear. Here we present the 3.7-angstrom cryo-electron microscopy structure of the yeast P-complex spliceosome immediately after exon ligation. The 3'-splice site AG dinucleotide is recognized through non-Watson-Crick pairing with the 5' splice site and the branch-point adenosine. After the branching reaction, protein factors work together to remodel the spliceosome and stabilize a conformation competent for 3'-splice site docking, thereby promoting exon ligation. The structure accounts for the strict conservation of the GU and AG dinucleotides at the 5' and 3' ends of introns and provides insight into the catalytic mechanism of exon ligation.
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Affiliation(s)
- Max E Wilkinson
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK.
| | - Sebastian M Fica
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
| | | | | | | | - Kiyoshi Nagai
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK.
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30
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snRNP proteins in health and disease. Semin Cell Dev Biol 2017; 79:92-102. [PMID: 29037818 DOI: 10.1016/j.semcdb.2017.10.011] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2017] [Revised: 10/09/2017] [Accepted: 10/12/2017] [Indexed: 01/16/2023]
Abstract
Split gene architecture of most human genes requires removal of intervening sequences by mRNA splicing that occurs on large multiprotein complexes called spliceosomes. Mutations compromising several spliceosomal components have been recorded in degenerative syndromes and haematological neoplasia, thereby highlighting the importance of accurate splicing execution in homeostasis of assorted adult tissues. Moreover, insufficient splicing underlies defective development of craniofacial skeleton and upper extremities. This review summarizes recent advances in the understanding of splicing factor function deduced from cryo-EM structures. We combine these data with the characterization of splicing factors implicated in hereditary or somatic disorders, with a focus on potential functional consequences the mutations may elicit in spliceosome assembly and/or performance. Given aberrant splicing or perturbations in splicing efficiency substantially underpin disease pathogenesis, profound understanding of the mis-splicing principles may open new therapeutic vistas. In three major sections dedicated to retinal dystrophies, hereditary acrofacial syndromes, and haematological malignancies, we delineate the noticeable variety of conditions associated with dysfunctional splicing and accentuate recurrent patterns in splicing defects.
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31
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Fica SM, Nagai K. Cryo-electron microscopy snapshots of the spliceosome: structural insights into a dynamic ribonucleoprotein machine. Nat Struct Mol Biol 2017; 24:791-799. [PMID: 28981077 DOI: 10.1038/nsmb.3463] [Citation(s) in RCA: 129] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2017] [Accepted: 08/10/2017] [Indexed: 12/18/2022]
Abstract
The spliceosome excises introns from pre-messenger RNAs using an RNA-based active site that is cradled by a dynamic protein scaffold. A recent revolution in cryo-electron microscopy (cryo-EM) has led to near-atomic-resolution structures of key spliceosome complexes that provide insight into the mechanism of activation, splice site positioning, catalysis, protein rearrangements and ATPase-mediated dynamics of the active site. The cryo-EM structures rationalize decades of observations from genetic and biochemical studies and provide a molecular framework for future functional studies.
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32
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Mechanistic insights into precursor messenger RNA splicing by the spliceosome. Nat Rev Mol Cell Biol 2017; 18:655-670. [DOI: 10.1038/nrm.2017.86] [Citation(s) in RCA: 234] [Impact Index Per Article: 33.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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33
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Scheres SH, Nagai K. CryoEM structures of spliceosomal complexes reveal the molecular mechanism of pre-mRNA splicing. Curr Opin Struct Biol 2017; 46:130-139. [PMID: 28888105 DOI: 10.1016/j.sbi.2017.08.001] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2017] [Revised: 07/26/2017] [Accepted: 08/07/2017] [Indexed: 01/09/2023]
Abstract
The spliceosome is an intricate molecular machine which catalyses the removal of introns from eukaryotic mRNA precursors by two trans-esterification reactions (branching and exon ligation) to produce mature mRNA with uninterrupted protein coding sequences. The structures of the spliceosome in several key states determined by electron cryo-microscopy have greatly advanced our understanding of its molecular mechanism. The catalytic RNA core is formed during the activation of the fully assembled B to Bact complex and remains largely unchanged throughout the splicing cycle. RNA helicases and step specific factors regulate docking and undocking of the substrates (branch site and 3' splice site) to the single RNA-based active site to catalyse the two trans-esterification reactions.
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Affiliation(s)
- Sjors Hw Scheres
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, United Kingdom.
| | - Kiyoshi Nagai
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, United Kingdom.
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34
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Costa M, Walbott H, Monachello D, Westhof E, Michel F. Crystal structures of a group II intron lariat primed for reverse splicing. Science 2017; 354:354/6316/aaf9258. [PMID: 27934709 DOI: 10.1126/science.aaf9258] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2016] [Accepted: 10/27/2016] [Indexed: 12/28/2022]
Abstract
The 2'-5' branch of nuclear premessenger introns is believed to have been inherited from self-splicing group II introns, which are retrotransposons of bacterial origin. Our crystal structures at 3.4 and 3.5 angstrom of an excised group II intron in branched ("lariat") form show that the 2'-5' branch organizes a network of active-site tertiary interactions that position the intron terminal 3'-hydroxyl group into a configuration poised to initiate reverse splicing, the first step in retrotransposition. Moreover, the branchpoint and flanking helices must undergo a base-pairing switch after branch formation. A group II-based model of the active site of the nuclear splicing machinery (the spliceosome) is proposed. The crucial role of the lariat conformation in active-site assembly and catalysis explains its prevalence in modern splicing.
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Affiliation(s)
- Maria Costa
- Group II introns as ribozymes and retrotransposons, Institute for Integrative Biology of the Cell (I2BC), UMR 9198 CNRS, Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA), University Paris-Sud, University Paris-Saclay, 1 Avenue de la Terrasse, Bâtiment 26, 91198 Gif-sur-Yvette cedex, France.
| | - Hélène Walbott
- Structure and Dynamics of RNA, I2BC, UMR 9198 CNRS, CEA, University Paris-Sud, University Paris-Saclay, 91198 Gif-sur-Yvette cedex, France
| | - Dario Monachello
- Group II introns as ribozymes and retrotransposons, Institute for Integrative Biology of the Cell (I2BC), UMR 9198 CNRS, Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA), University Paris-Sud, University Paris-Saclay, 1 Avenue de la Terrasse, Bâtiment 26, 91198 Gif-sur-Yvette cedex, France
| | - Eric Westhof
- Architecture and Reactivity of RNA, Institute of Molecular and Cellular Biology of the CNRS, University of Strasbourg, 15 rue René Descartes, 67084 Strasbourg, France
| | - François Michel
- Group II introns as ribozymes and retrotransposons, Institute for Integrative Biology of the Cell (I2BC), UMR 9198 CNRS, Commissariat à l'Energie Atomique et aux Energies Alternatives (CEA), University Paris-Sud, University Paris-Saclay, 1 Avenue de la Terrasse, Bâtiment 26, 91198 Gif-sur-Yvette cedex, France
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35
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Shi Y. The Spliceosome: A Protein-Directed Metalloribozyme. J Mol Biol 2017; 429:2640-2653. [PMID: 28733144 DOI: 10.1016/j.jmb.2017.07.010] [Citation(s) in RCA: 69] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2017] [Revised: 07/13/2017] [Accepted: 07/14/2017] [Indexed: 11/15/2022]
Abstract
Pre-mRNA splicing is executed by the ribonucleoprotein machinery spliceosome. Nearly 40 years after the discovery of pre-mRNA splicing, the atomic structure of the spliceosome has finally come to light. Four distinct conformational states of the yeast spliceosome have been captured at atomic or near-atomic resolutions. Two catalytic metal ions at the active site are specifically coordinated by the U6 small nuclear RNA (snRNA) and catalyze both the branching reaction and the exon ligation. Of the three snRNAs in the fully assembled spliceosome, U5 and U6, along with 30 contiguous nucleotides of U2 at its 5'-end, remain structurally rigid throughout the splicing reaction. The rigidity of these RNA elements is safeguarded by Prp8 and 16 core protein components, which maintain the same overall conformation in all structurally characterized spliceosomes during the splicing reaction. Only the sequences downstream of nucleotide 30 of U2 snRNA are mobile; their movement, directed by the protein components, delivers the intron branch site into the close proximity of the 5'-splice site for the branching reaction. A set of additional structural rearrangement is required for exon ligation, and the lariat junction is moved out of the active site for recruitment of the 3'-splice site and 3'-exon. The spliceosome is proven to be a protein-directed metalloribozyme.
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Affiliation(s)
- Yigong Shi
- Beijing Advanced Innovation Center for Structural Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China; Institute of Biology, Westlake Institute for Advanced Study, 18 Shilongshan Road, Xihu District, Hangzhou 310064, Zhejiang Province, Province, China.
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36
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Plaschka C, Lin PC, Nagai K. Structure of a pre-catalytic spliceosome. Nature 2017; 546:617-621. [PMID: 28530653 PMCID: PMC5503131 DOI: 10.1038/nature22799] [Citation(s) in RCA: 160] [Impact Index Per Article: 22.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2017] [Accepted: 05/02/2017] [Indexed: 12/12/2022]
Abstract
Intron removal requires assembly of the spliceosome on precursor mRNA (pre-mRNA) and extensive remodelling to form the spliceosome's catalytic centre. Here we report the cryo-electron microscopy structure of the yeast Saccharomyces cerevisiae pre-catalytic B complex spliceosome at near-atomic resolution. The mobile U2 small nuclear ribonucleoprotein particle (snRNP) associates with U4/U6.U5 tri-snRNP through the U2/U6 helix II and an interface between U4/U6 di-snRNP and the U2 snRNP SF3b-containing domain, which also transiently contacts the helicase Brr2. The 3' region of the U2 snRNP is flexibly attached to the SF3b-containing domain and protrudes over the concave surface of tri-snRNP, where the U1 snRNP may reside before its release from the pre-mRNA 5' splice site. The U6 ACAGAGA sequence forms a hairpin that weakly tethers the 5' splice site. The B complex proteins Prp38, Snu23 and Spp381 bind the Prp8 N-terminal domain and stabilize U6 ACAGAGA stem-pre-mRNA and Brr2-U4 small nuclear RNA interactions. These results provide important insights into the events leading to active site formation.
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MESH Headings
- Base Sequence
- Biocatalysis
- Catalytic Domain
- Cryoelectron Microscopy
- Introns/genetics
- Models, Biological
- Models, Molecular
- Nuclear Proteins/chemistry
- Nuclear Proteins/metabolism
- Protein Binding
- Protein Domains
- Protein Stability
- RNA Helicases/chemistry
- RNA Helicases/metabolism
- RNA Helicases/ultrastructure
- RNA Precursors/genetics
- RNA Precursors/metabolism
- RNA Precursors/ultrastructure
- RNA Splice Sites/genetics
- RNA Splicing
- RNA Splicing Factors/chemistry
- RNA Splicing Factors/metabolism
- RNA, Small Nuclear/chemistry
- RNA, Small Nuclear/metabolism
- Ribonucleoprotein, U2 Small Nuclear/chemistry
- Ribonucleoprotein, U2 Small Nuclear/metabolism
- Ribonucleoprotein, U4-U6 Small Nuclear/chemistry
- Ribonucleoprotein, U4-U6 Small Nuclear/metabolism
- Ribonucleoprotein, U5 Small Nuclear/chemistry
- Ribonucleoprotein, U5 Small Nuclear/metabolism
- Ribonucleoproteins, Small Nuclear/chemistry
- Ribonucleoproteins, Small Nuclear/metabolism
- Saccharomyces cerevisiae/chemistry
- Saccharomyces cerevisiae/genetics
- Saccharomyces cerevisiae Proteins/chemistry
- Saccharomyces cerevisiae Proteins/metabolism
- Saccharomyces cerevisiae Proteins/ultrastructure
- Spliceosomes/chemistry
- Spliceosomes/metabolism
- Spliceosomes/ultrastructure
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Affiliation(s)
- Clemens Plaschka
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, United Kingdom
| | - Pei-Chun Lin
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, United Kingdom
| | - Kiyoshi Nagai
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, United Kingdom
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37
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Sidarovich A, Will CL, Anokhina MM, Ceballos J, Sievers S, Agafonov DE, Samatov T, Bao P, Kastner B, Urlaub H, Waldmann H, Lührmann R. Identification of a small molecule inhibitor that stalls splicing at an early step of spliceosome activation. eLife 2017; 6. [PMID: 28300534 PMCID: PMC5354520 DOI: 10.7554/elife.23533] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2016] [Accepted: 02/26/2017] [Indexed: 11/13/2022] Open
Abstract
Small molecule inhibitors of pre-mRNA splicing are important tools for identifying new spliceosome assembly intermediates, allowing a finer dissection of spliceosome dynamics and function. Here, we identified a small molecule that inhibits human pre-mRNA splicing at an intermediate stage during conversion of pre-catalytic spliceosomal B complexes into activated Bact complexes. Characterization of the stalled complexes (designated B028) revealed that U4/U6 snRNP proteins are released during activation before the U6 Lsm and B-specific proteins, and before recruitment and/or stable incorporation of Prp19/CDC5L complex and other Bact complex proteins. The U2/U6 RNA network in B028 complexes differs from that of the Bact complex, consistent with the idea that the catalytic RNA core forms stepwise during the B to Bact transition and is likely stabilized by the Prp19/CDC5L complex and related proteins. Taken together, our data provide new insights into the RNP rearrangements and extensive exchange of proteins that occurs during spliceosome activation. DOI:http://dx.doi.org/10.7554/eLife.23533.001
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Affiliation(s)
- Anzhalika Sidarovich
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Cindy L Will
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Maria M Anokhina
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Javier Ceballos
- Department of Chemical Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | - Sonja Sievers
- Compound Management and Screening Center, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | - Dmitry E Agafonov
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Timur Samatov
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Penghui Bao
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Berthold Kastner
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Henning Urlaub
- Bioanalytics Group, Institute for Clinical Chemistry Göttingen, University Medical Center, Göttingen, Germany
| | - Herbert Waldmann
- Department of Chemical Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | - Reinhard Lührmann
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
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38
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Role of Cwc24 in the First Catalytic Step of Splicing and Fidelity of 5' Splice Site Selection. Mol Cell Biol 2017; 37:MCB.00580-16. [PMID: 27994011 DOI: 10.1128/mcb.00580-16] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2016] [Accepted: 12/11/2016] [Indexed: 12/17/2022] Open
Abstract
Cwc24 is an essential splicing factor but only transiently associates with the spliceosome, with an unknown function. The protein contains a RING finger and a zinc finger domain in the carboxyl terminus. The human ortholog of Cwc24, RNF113A, has been associated with the disorder trichothiodystrophy. Here, we show that the zinc finger domain is essential for Cwc24 function, while the RING finger domain is dispensable. Cwc24 binds to the spliceosome after the Prp19-associated complex and is released upon Prp2 action. Cwc24 is not required for Prp2-mediated remodeling of the spliceosome, but the spliceosome becomes inactive if remodeling occurs before the addition of Cwc24. Cwc24 binds directly to pre-mRNA at the 5' splice site, spanning the splice junction. In the absence of Cwc24, U5 and U6 modes of interaction with the 5' splice site are altered, and splicing is very inefficient, with aberrant cleavage at the 5' splice site. Our data suggest roles for Cwc24 in orchestrating organization of the spliceosome into an active configuration prior to Prp2-mediated spliceosome remodeling and in promoting specific interaction of U5 and U6 with the 5' splice site for fidelity of 5' splice site selection.
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39
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Bertram K, Agafonov DE, Liu WT, Dybkov O, Will CL, Hartmuth K, Urlaub H, Kastner B, Stark H, Lührmann R. Cryo-EM structure of a human spliceosome activated for step 2 of splicing. Nature 2017; 542:318-323. [DOI: 10.1038/nature21079] [Citation(s) in RCA: 179] [Impact Index Per Article: 25.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2016] [Accepted: 01/04/2017] [Indexed: 12/18/2022]
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40
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Fica SM, Oubridge C, Galej WP, Wilkinson ME, Bai XC, Newman AJ, Nagai K. Structure of a spliceosome remodelled for exon ligation. Nature 2017; 542:377-380. [PMID: 28076345 PMCID: PMC5321579 DOI: 10.1038/nature21078] [Citation(s) in RCA: 129] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2016] [Accepted: 01/04/2017] [Indexed: 12/11/2022]
Abstract
The spliceosome excises introns from pre-mRNAs in two sequential transesterifications – branching and exon ligation1 – catalysed at a single catalytic metal site in U6 snRNA2,3. The recent structures of the spliceosomal C complex4,5 with the cleaved 5’-exon and lariat—3’-exon bound to the catalytic centre revealed that branching-specific factors such as Cwc25 lock the branch helix into position for nucleophilic attack of the branch adenosine at the 5’-splice site. Furthermore, the ATPase Prp16 is positioned to bind and translocate the intron downstream of the branch point to destabilize branching-specific factors and release the branch helix from the active site4. Here we present the 3.8Å cryo-EM structure of a Saccharomyces cerevisiae spliceosome stalled after Prp16-mediated remodelling but prior to exon ligation. While the U6 snRNA catalytic core remains firmly held in the active site cavity of Prp8 by proteins common to both steps, the branch helix has rotated by 75 degrees compared to complex C and is stabilized into a new position by Prp17, Cef1, and the reoriented Prp8 RNaseH domain. This rotation of the branch helix removes the branch adenosine from the catalytic core, creates a space for 3’-exon docking, and restructures the pairing of the 5’-splice site with the U6 snRNA ACAGAGA region. Slu7 and Prp18, which promote exon ligation, bind together to the Prp8 RNaseH domain. The ATPase Prp22, bound to Prp8 in place of Prp16, could interact with the 3’-exon, suggesting a possible basis for mRNA release after exon ligation6,7. Together with the C complex structure4, our new C* complex structure reveals the two major conformations of the spliceosome during the catalytic stages of splicing.
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Affiliation(s)
- Sebastian M Fica
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
| | - Chris Oubridge
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
| | - Wojciech P Galej
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
| | - Max E Wilkinson
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
| | - Xiao-Chen Bai
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
| | - Andrew J Newman
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
| | - Kiyoshi Nagai
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK
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41
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Yan C, Wan R, Bai R, Huang G, Shi Y. Structure of a yeast step II catalytically activated spliceosome. Science 2016; 355:149-155. [PMID: 27980089 DOI: 10.1126/science.aak9979] [Citation(s) in RCA: 117] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2016] [Accepted: 12/05/2016] [Indexed: 12/30/2022]
Abstract
Each cycle of precursor messenger RNA (pre-mRNA) splicing comprises two sequential reactions, first freeing the 5' exon and generating an intron lariat-3' exon and then ligating the two exons and releasing the intron lariat. The second reaction is executed by the step II catalytically activated spliceosome (known as the C* complex). Here, we present the cryo-electron microscopy structure of a C* complex from Saccharomyces cerevisiae at an average resolution of 4.0 angstroms. Compared with the preceding spliceosomal complex (C complex), the lariat junction has been translocated by 15 to 20 angstroms to vacate space for the incoming 3'-exon sequences. The step I splicing factors Cwc25 and Yju2 have been dissociated from the active site. Two catalytic motifs from Prp8 (the 1585 loop and the β finger of the ribonuclease H-like domain), along with the step II splicing factors Prp17 and Prp18 and other surrounding proteins, are poised to assist the second transesterification. These structural features, together with those reported for other spliceosomal complexes, yield a near-complete mechanistic picture on the splicing cycle.
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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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42
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Sun C, Rigo N, Fabrizio P, Kastner B, Lührmann R. A protein map of the yeast activated spliceosome as obtained by electron microscopy. RNA (NEW YORK, N.Y.) 2016; 22:1427-40. [PMID: 27368340 PMCID: PMC4986897 DOI: 10.1261/rna.057778.116] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/16/2016] [Accepted: 05/31/2016] [Indexed: 05/09/2023]
Abstract
We have elucidated the spatial arrangement of proteins and snRNP subunits within the purified spliceosomal B(act) complex from Saccharomyces cerevisiae, using negative-stain immunoelectron microscopy. The B(act) spliceosome exhibits a mushroom-like shape with a main body connected to a foot and a steep and a shallow slope. The U5 core components, including proteins Snu114 and Prp8, are located in the main body and foot, while Brr2 is on the shallow slope. U2 snRNP components and the RNA helicase Prp2 were predominantly located in the upper regions of both slopes. While several proteins of the "nineteen complex" are located on the steep slope, Prp19, Cef1, and the U6 snRNA-binding protein Cwc2 are on the main body. Our results also indicate that the catalytic core RNP of the spliceosome resides in its main body. We thus assign distinct domains of the B(act) complex to its snRNP and protein components, and we provide first structural insights into the remodeling events at the spliceosome during its transformation from the B to the B(act) complex.
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Affiliation(s)
- Chengfu Sun
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
| | - Norbert Rigo
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
| | - Patrizia Fabrizio
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
| | - Berthold Kastner
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
| | - Reinhard Lührmann
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
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43
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Rauhut R, Fabrizio P, Dybkov O, Hartmuth K, Pena V, Chari A, Kumar V, Lee CT, Urlaub H, Kastner B, Stark H, Lührmann R. Molecular architecture of the Saccharomyces cerevisiae activated spliceosome. Science 2016; 353:1399-1405. [PMID: 27562955 DOI: 10.1126/science.aag1906] [Citation(s) in RCA: 139] [Impact Index Per Article: 17.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2016] [Accepted: 08/18/2016] [Indexed: 12/30/2022]
Abstract
The activated spliceosome (Bact) is in a catalytically inactive state and is remodeled into a catalytically active machine by the RNA helicase Prp2, but the mechanism is unclear. Here, we describe a 3D electron cryomicroscopy structure of the Saccharomyces cerevisiae Bact complex at 5.8-angstrom resolution. Our model reveals that in Bact, the catalytic U2/U6 RNA-Prp8 ribonucleoprotein core is already established, and the 5' splice site (ss) is oriented for step 1 catalysis but occluded by protein. The first-step nucleophile-the branchsite adenosine-is sequestered within the Hsh155 HEAT domain and is held 50 angstroms away from the 5'ss. Our structure suggests that Prp2 adenosine triphosphatase-mediated remodeling leads to conformational changes in Hsh155's HEAT domain that liberate the first-step reactants for catalysis.
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Affiliation(s)
- Reinhard Rauhut
- Department of Cellular Biochemistry, Max Planck Institute (MPI) for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany
| | - Patrizia Fabrizio
- Department of Cellular Biochemistry, Max Planck Institute (MPI) for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany
| | - Olexandr Dybkov
- Department of Cellular Biochemistry, Max Planck Institute (MPI) for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany
| | - Klaus Hartmuth
- Department of Cellular Biochemistry, Max Planck Institute (MPI) for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany
| | - Vladimir Pena
- Research Group Macromolecular Crystallography, MPI for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
| | - Ashwin Chari
- 3D Electron Cryomicroscopy Group, MPI for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany
| | - Vinay Kumar
- Department of Cellular Biochemistry, Max Planck Institute (MPI) for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany
| | - Chung-Tien Lee
- Bioanalytical Mass Spectrometry, MPI for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany. Bioanalytics Group, Institute for Clinical Chemistry, University Medical Center, Göttingen, Robert-Koch-Straße 40, D-37075 Göttingen, Germany
| | - Henning Urlaub
- Bioanalytical Mass Spectrometry, MPI for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany. Bioanalytics Group, Institute for Clinical Chemistry, University Medical Center, Göttingen, Robert-Koch-Straße 40, D-37075 Göttingen, Germany
| | - Berthold Kastner
- Department of Cellular Biochemistry, Max Planck Institute (MPI) for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany.
| | - Holger Stark
- 3D Electron Cryomicroscopy Group, MPI for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany. Department of 3D Electron Cryomicroscopy, Georg-August Universität, Göttingen, Justus von-Liebig-Weg 11, D-37077 Germany.
| | - Reinhard Lührmann
- Department of Cellular Biochemistry, Max Planck Institute (MPI) for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany.
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44
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Cryo-EM structure of the spliceosome immediately after branching. Nature 2016; 537:197-201. [PMID: 27459055 PMCID: PMC5156311 DOI: 10.1038/nature19316] [Citation(s) in RCA: 177] [Impact Index Per Article: 22.1] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2016] [Accepted: 07/19/2016] [Indexed: 12/11/2022]
Abstract
Precursor mRNA (pre-mRNA) splicing proceeds by two consecutive transesterification reactions via a lariat-intron intermediate. Here we present the 3.8 Å cryo-electron microscopy structure of the spliceosome immediately after lariat formation. The 5'-splice site is cleaved but remains close to the catalytic Mg2+ site in the U2/U6 small nuclear RNA (snRNA) triplex, and the 5'-phosphate of the intron nucleotide G(+1) is linked to the branch adenosine 2'OH. The 5'-exon is held between the Prp8 amino-terminal and linker domains, and base-pairs with U5 snRNA loop 1. Non-Watson-Crick interactions between the branch helix and 5'-splice site dock the branch adenosine into the active site, while intron nucleotides +3 to +6 base-pair with the U6 snRNA ACAGAGA sequence. Isy1 and the step-one factors Yju2 and Cwc25 stabilize docking of the branch helix. The intron downstream of the branch site emerges between the Prp8 reverse transcriptase and linker domains and extends towards the Prp16 helicase, suggesting a plausible mechanism of remodelling before exon ligation.
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45
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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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46
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Boesler C, Rigo N, Anokhina MM, Tauchert MJ, Agafonov DE, Kastner B, Urlaub H, Ficner R, Will CL, Lührmann R. A spliceosome intermediate with loosely associated tri-snRNP accumulates in the absence of Prp28 ATPase activity. Nat Commun 2016; 7:11997. [PMID: 27377154 PMCID: PMC4935976 DOI: 10.1038/ncomms11997] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2015] [Accepted: 05/20/2016] [Indexed: 11/17/2022] Open
Abstract
The precise role of the spliceosomal DEAD-box protein Prp28 in higher eukaryotes remains unclear. We show that stable tri-snRNP association during pre-catalytic spliceosomal B complex formation is blocked by a dominant-negative hPrp28 mutant lacking ATPase activity. Complexes formed in the presence of ATPase-deficient hPrp28 represent a novel assembly intermediate, the pre-B complex, that contains U1, U2 and loosely associated tri-snRNP and is stalled before disruption of the U1/5′ss base pairing interaction, consistent with a role for hPrp28 in the latter. Pre-B and B complexes differ structurally, indicating that stable tri-snRNP integration is accompanied by substantial rearrangements in the spliceosome. Disruption of the U1/5′ss interaction alone is not sufficient to bypass the block by ATPase-deficient hPrp28, suggesting hPrp28 has an additional function at this stage of splicing. Our data provide new insights into the function of Prp28 in higher eukaryotes, and the requirements for stable tri-snRNP binding during B complex formation. The assembly of the splicesome involves several distinct stages that require the sequential action of DExD/H-box RNA helicases. Here, the authors uncover a new intermediate, the pre-B complex, that accumulates in the presence of an inactive form of the DEAD-box protein Prp28.
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Affiliation(s)
- Carsten Boesler
- Department of Cellular Biochemistry, MPI for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany
| | - Norbert Rigo
- Department of Cellular Biochemistry, MPI for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany
| | - Maria M Anokhina
- Department of Cellular Biochemistry, MPI for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany
| | - Marcel J Tauchert
- Department of Molecular Structural Biology, Institute for Microbiology and Genetics, GZMB, Georg-August-Universität Göttingen, Justus-von-Liebig-Weg 11, D-37077 Göttingen, Germany
| | - Dmitry E Agafonov
- Department of Cellular Biochemistry, MPI for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany
| | - Berthold Kastner
- Department of Cellular Biochemistry, MPI for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany
| | - Henning Urlaub
- Bioanalytical Mass Spectrometry Group, MPI for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany.,Bioanalytics Group, Institute for Clinical Chemistry, University Medical Center Göttingen, Robert-Koch-Straße 40, D-37075 Göttingen, Germany
| | - Ralf Ficner
- Department of Molecular Structural Biology, Institute for Microbiology and Genetics, GZMB, Georg-August-Universität Göttingen, Justus-von-Liebig-Weg 11, D-37077 Göttingen, Germany
| | - Cindy L Will
- Department of Cellular Biochemistry, MPI for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany
| | - Reinhard Lührmann
- Department of Cellular Biochemistry, MPI for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany
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47
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Mayerle M, Guthrie C. Prp8 retinitis pigmentosa mutants cause defects in the transition between the catalytic steps of splicing. RNA (NEW YORK, N.Y.) 2016; 22:793-809. [PMID: 26968627 PMCID: PMC4836653 DOI: 10.1261/rna.055459.115] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2015] [Accepted: 02/11/2016] [Indexed: 05/14/2023]
Abstract
Pre-mRNA splicing must occur with high fidelity and efficiency for proper gene expression. The spliceosome uses DExD/H box helicases to promote on-pathway interactions while simultaneously minimizing errors. Prp8 and Snu114, an EF2-like GTPase, regulate the activity of the Brr2 helicase, promoting RNA unwinding by Brr2 at appropriate points in the splicing cycle and repressing it at others. Mutations linked to retinitis pigmentosa (RP), a disease that causes blindness in humans, map to the Brr2 regulatory region of Prp8. Previous in vitro studies of homologous mutations in Saccharomyces cerevisiaes how that Prp8-RP mutants cause defects in spliceosome activation. Here we show that a subset of RP mutations in Prp8 also causes defects in the transition between the first and second catalytic steps of splicing. Though Prp8-RP mutants do not cause defects in splicing fidelity, they result in an overall decrease in splicing efficiency. Furthermore, genetic analyses link Snu114 GTP/GDP occupancy to Prp8-dependent regulation of Brr2. Our results implicate the transition between the first and second catalytic steps as a critical place in the splicing cycle where Prp8-RP mutants influence splicing efficiency. The location of the Prp8-RP mutants, at the "hinge" that links the Prp8 Jab1-MPN regulatory "tail" to the globular portion of the domain, suggests that these Prp8-RP mutants inhibit regulated movement of the Prp8 Jab1/MPN domain into the Brr2 RNA binding channel to transiently inhibit Brr2. Therefore, in Prp8-linked RP, disease likely results not only from defects in spliceosome assembly and activation, but also because of defects in splicing catalysis.
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Affiliation(s)
- Megan Mayerle
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California 94143, USA
| | - Christine Guthrie
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California 94143, USA
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48
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Agafonov DE, Kastner B, Dybkov O, Hofele RV, Liu WT, Urlaub H, Lührmann R, Stark H. Molecular architecture of the human U4/U6.U5 tri-snRNP. Science 2016; 351:1416-20. [PMID: 26912367 DOI: 10.1126/science.aad2085] [Citation(s) in RCA: 143] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2015] [Accepted: 02/04/2016] [Indexed: 12/24/2022]
Abstract
The U4/U6.U5 triple small nuclear ribonucleoprotein (tri-snRNP) is a major spliceosome building block. We obtained a three-dimensional structure of the 1.8-megadalton human tri-snRNP at a resolution of 7 angstroms using single-particle cryo-electron microscopy (cryo-EM). We fit all known high-resolution structures of tri-snRNP components into the EM density map and validated them by protein cross-linking. Our model reveals how the spatial organization of Brr2 RNA helicase prevents premature U4/U6 RNA unwinding in isolated human tri-snRNPs and how the ubiquitin C-terminal hydrolase-like protein Sad1 likely tethers the helicase Brr2 to its preactivation position. Comparison of our model with cryo-EM three-dimensional structures of the Saccharomyces cerevisiae tri-snRNP and Schizosaccharomyces pombe spliceosome indicates that Brr2 undergoes a marked conformational change during spliceosome activation, and that the scaffolding protein Prp8 is also rearranged to accommodate the spliceosome's catalytic RNA network.
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Affiliation(s)
- Dmitry E Agafonov
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, D-37077 Göttingen, Germany
| | - Berthold Kastner
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, D-37077 Göttingen, Germany
| | - Olexandr Dybkov
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, D-37077 Göttingen, Germany
| | - Romina V Hofele
- Bioanalytical Mass Spectrometry, Max Planck Institute for Biophysical Chemistry, D-37077 Göttingen, Germany. Bioanalytics Group, Institute for Clinical Chemistry, University Medical Center Göttingen, D-37075 Göttingen, Germany
| | - Wen-Ti Liu
- Department of 3D Electron Cryomicroscopy, Georg-August Universität Göttingen, D-37077 Göttingen, Germany. Department of Structural Dynamics, Max Planck Institute for Biophysical Chemistry, D-37077 Göttingen, Germany
| | - Henning Urlaub
- Bioanalytical Mass Spectrometry, Max Planck Institute for Biophysical Chemistry, D-37077 Göttingen, Germany. Bioanalytics Group, Institute for Clinical Chemistry, University Medical Center Göttingen, D-37075 Göttingen, Germany.
| | - Reinhard Lührmann
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, D-37077 Göttingen, Germany.
| | - Holger Stark
- Department of 3D Electron Cryomicroscopy, Georg-August Universität Göttingen, D-37077 Göttingen, Germany. Department of Structural Dynamics, Max Planck Institute for Biophysical Chemistry, D-37077 Göttingen, Germany.
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49
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Nguyen THD, Galej WP, Bai XC, Oubridge C, Newman AJ, Scheres SHW, Nagai K. Cryo-EM structure of the yeast U4/U6.U5 tri-snRNP at 3.7 Å resolution. Nature 2016; 530:298-302. [PMID: 26829225 PMCID: PMC4762201 DOI: 10.1038/nature16940] [Citation(s) in RCA: 162] [Impact Index Per Article: 20.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2015] [Accepted: 12/18/2015] [Indexed: 12/12/2022]
Abstract
U4/U6.U5 tri-snRNP represents a substantial part of the spliceosome before activation. A cryoEM structure of Saccharomyces cerevisiae U4/U6.U5 tri-snRNP at 3.7Å resolution led to an essentially complete atomic model comprising 30 proteins plus U4/U6 and U5 snRNAs. The structure reveals striking interweaving interactions of the protein and RNA components including extended polypeptides penetrating into subunit interfaces. The invariant ACAGAGA sequence of U6 snRNA, which base-pairs with the 5′-splice site during catalytic activation, forms a hairpin stabilised by Dib1 and Prp8 while the adjacent nucleotides interact with the exon binding loop 1 of U5 snRNA. Snu114 harbours GTP but its putative catalytic histidine is held away from the γ-phosphate by hydrogen bonding to a tyrosine in Prp8’s N-terminal domain. Mutation of this histidine to alanine has no detectable effect on yeast growth. The structure provides important new insights into the spliceosome activation process leading to the formation of the catalytic centre.
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Affiliation(s)
| | - Wojciech P Galej
- MRC Laboratory of Molecular Biology Francis Crick Avenue Cambridge CB2 0QH UK
| | - Xiao-Chen Bai
- MRC Laboratory of Molecular Biology Francis Crick Avenue Cambridge CB2 0QH UK
| | - Chris Oubridge
- MRC Laboratory of Molecular Biology Francis Crick Avenue Cambridge CB2 0QH UK
| | - Andrew J Newman
- MRC Laboratory of Molecular Biology Francis Crick Avenue Cambridge CB2 0QH UK
| | - Sjors H W Scheres
- MRC Laboratory of Molecular Biology Francis Crick Avenue Cambridge CB2 0QH UK
| | - Kiyoshi Nagai
- MRC Laboratory of Molecular Biology Francis Crick Avenue Cambridge CB2 0QH UK
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50
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CryoEM structures of two spliceosomal complexes: starter and dessert at the spliceosome feast. Curr Opin Struct Biol 2016; 36:48-57. [PMID: 26803803 PMCID: PMC4830896 DOI: 10.1016/j.sbi.2015.12.005] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2015] [Accepted: 12/21/2015] [Indexed: 12/31/2022]
Abstract
Recent advances in cryoEM are revolutionizing our understanding of how molecular machines function. The structure of Saccharomyces cerevisiae U4/U6.U5 tri-snRNP has been revealed. The structure of Schizosaccharomyces pombe U2.U6.U5 spliceosomal complex has been revealed. These structures greatly advanced our understanding of the mechanism of pre-mRNA splicing.
The spliceosome is formed on pre-mRNA substrates from five small nuclear ribonucleoprotein particles (U1, U2, U4/U6 and U5 snRNPs), and numerous non-snRNP factors. Saccharomyces cerevisiae U4/U6.U5 tri-snRNP comprises U5 snRNA, U4/U6 snRNA duplex and approximately 30 proteins and represents a substantial part of the spliceosome before activation. Schizosaccharomyces pombe U2.U6.U5 spliceosomal complex is a post-catalytic intron lariat spliceosome containing U2 and U5 snRNPs, NTC (nineteen complex), NTC-related proteins (NTR), U6 snRNA, and an RNA intron lariat. Two recent papers describe near-complete atomic structures of these complexes based on cryoEM single-particle analysis. The U4/U6.U5 tri-snRNP structure provides crucial insight into the activation mechanism of the spliceosome. The U2.U6.U5 complex reveals the striking architecture of NTC and NTR and important features of the group II intron-like catalytic RNA core remaining after spliced mRNA is released. These two structures greatly advance our understanding of the mechanism of pre-mRNA splicing.
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