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Abrhámová K, Groušlová M, Valentová A, Hao X, Liu B, Převorovský M, Gahura O, Půta F, Sunnerhagen P, Folk P. Truncating the spliceosomal 'rope protein' Prp45 results in Htz1 dependent phenotypes. RNA Biol 2024; 21:1-17. [PMID: 38711165 PMCID: PMC11085953 DOI: 10.1080/15476286.2024.2348896] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/24/2024] [Indexed: 05/08/2024] Open
Abstract
Spliceosome assembly contributes an important but incompletely understood aspect of splicing regulation. Prp45 is a yeast splicing factor which runs as an extended fold through the spliceosome, and which may be important for bringing its components together. We performed a whole genome analysis of the genetic interaction network of the truncated allele of PRP45 (prp45(1-169)) using synthetic genetic array technology and found chromatin remodellers and modifiers as an enriched category. In agreement with related studies, H2A.Z-encoding HTZ1, and the components of SWR1, INO80, and SAGA complexes represented prominent interactors, with htz1 conferring the strongest growth defect. Because the truncation of Prp45 disproportionately affected low copy number transcripts of intron-containing genes, we prepared strains carrying intronless versions of SRB2, VPS75, or HRB1, the most affected cases with transcription-related function. Intron removal from SRB2, but not from the other genes, partly repaired some but not all the growth phenotypes identified in the genetic screen. The interaction of prp45(1-169) and htz1Δ was detectable even in cells with SRB2 intron deleted (srb2Δi). The less truncated variant, prp45(1-330), had a synthetic growth defect with htz1Δ at 16°C, which also persisted in the srb2Δi background. Moreover, htz1Δ enhanced prp45(1-330) dependent pre-mRNA hyper-accumulation of both high and low efficiency splicers, genes ECM33 and COF1, respectively. We conclude that while the expression defects of low expression intron-containing genes contribute to the genetic interactome of prp45(1-169), the genetic interactions between prp45 and htz1 alleles demonstrate the sensitivity of spliceosome assembly, delayed in prp45(1-169), to the chromatin environment.
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Affiliation(s)
- Kateřina Abrhámová
- Department of Cell Biology, Faculty of Science, Charles University, Praha, Czech Republic
| | - Martina Groušlová
- Department of Cell Biology, Faculty of Science, Charles University, Praha, Czech Republic
| | - Anna Valentová
- Department of Cell Biology, Faculty of Science, Charles University, Praha, Czech Republic
| | - Xinxin Hao
- Department of Chemistry and Molecular Biology, University of Gothenburg, Gothenburg, Sweden
| | - Beidong Liu
- Department of Chemistry and Molecular Biology, University of Gothenburg, Gothenburg, Sweden
| | - Martin Převorovský
- Department of Cell Biology, Faculty of Science, Charles University, Praha, Czech Republic
| | - Ondřej Gahura
- Institute of Parasitology, Biology Centre, Czech Academy of Sciences, České Budějovice, Czech Republic
| | - František Půta
- Department of Cell Biology, Faculty of Science, Charles University, Praha, Czech Republic
| | - Per Sunnerhagen
- Department of Chemistry and Molecular Biology, University of Gothenburg, Gothenburg, Sweden
| | - Petr Folk
- Department of Cell Biology, Faculty of Science, Charles University, Praha, Czech Republic
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2
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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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3
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Manigrasso J, Chillón I, Genna V, Vidossich P, Somarowthu S, Pyle AM, De Vivo M, Marcia M. Visualizing group II intron dynamics between the first and second steps of splicing. Nat Commun 2020; 11:2837. [PMID: 32503992 PMCID: PMC7275048 DOI: 10.1038/s41467-020-16741-4] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2019] [Accepted: 05/18/2020] [Indexed: 12/21/2022] Open
Abstract
Group II introns are ubiquitous self-splicing ribozymes and retrotransposable elements evolutionarily and chemically related to the eukaryotic spliceosome, with potential applications as gene-editing tools. Recent biochemical and structural data have captured the intron in multiple conformations at different stages of catalysis. Here, we employ enzymatic assays, X-ray crystallography, and molecular simulations to resolve the spatiotemporal location and function of conformational changes occurring between the first and the second step of splicing. We show that the first residue of the highly-conserved catalytic triad is protonated upon 5’-splice-site scission, promoting a reversible structural rearrangement of the active site (toggling). Protonation and active site dynamics induced by the first step of splicing facilitate the progression to the second step. Our insights into the mechanism of group II intron splicing parallels functional data on the spliceosome, thus reinforcing the notion that these evolutionarily-related molecular machines share the same enzymatic strategy. Group II introns are self-splicing ribozymes. Here, the authors employ enzymatic assay, X-ray crystallography and molecular dynamics simulations to show that protonation of the group II intron catalytic triad plays an important role for the transition from the first to the second step of splicing.
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Affiliation(s)
- Jacopo Manigrasso
- Laboratory of Molecular Modelling & Drug Discovery, Istituto Italiano di Tecnologia, Via Morego 30, 16163, Genoa, Italy
| | - Isabel Chillón
- European Molecular Biology Laboratory (EMBL) Grenoble, 71 Avenue des Martyrs, Grenoble, 38042, France
| | - Vito Genna
- Department of Structural and Computational Biology, Institute for Research in Biomedicine (IRB), Parc Científic de Barcelona, C/ Baldiri Reixac 10-12, 08028, Barcelona, Spain
| | - Pietro Vidossich
- Laboratory of Molecular Modelling & Drug Discovery, Istituto Italiano di Tecnologia, Via Morego 30, 16163, Genoa, Italy
| | - Srinivas Somarowthu
- Department of Biochemistry & Molecular Biology, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Anna Marie Pyle
- Department of Molecular, Cellular and Developmental Biology, New Haven, CT, 06511, USA.,Department of Chemistry, Yale University, New Haven, CT, 06511, USA.,Howard Hughes Medical Institute, Chevy Chase, MD, 20815, USA
| | - Marco De Vivo
- Laboratory of Molecular Modelling & Drug Discovery, Istituto Italiano di Tecnologia, Via Morego 30, 16163, Genoa, Italy.
| | - Marco Marcia
- European Molecular Biology Laboratory (EMBL) Grenoble, 71 Avenue des Martyrs, Grenoble, 38042, France.
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4
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Kundinger SR, Bishof I, Dammer EB, Duong DM, Seyfried NT. Middle-Down Proteomics Reveals Dense Sites of Methylation and Phosphorylation in Arginine-Rich RNA-Binding Proteins. J Proteome Res 2020; 19:1574-1591. [PMID: 31994892 DOI: 10.1021/acs.jproteome.9b00633] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Post-translational modifications (PTMs) within arginine (Arg)-rich RNA-binding proteins, such as phosphorylation and methylation, regulate multiple steps in RNA metabolism. However, the identification of PTMs within Arg-rich domains with complete trypsin digestion is extremely challenging due to the high density of Arg residues within these proteins. Here, we report a middle-down proteomic approach coupled with electron-transfer dissociation (ETD) mass spectrometry to map previously unknown sites of phosphorylation and methylation within the Arg-rich domains of U1-70K and structurally similar RNA-binding proteins from nuclear extracts of human embryonic kidney (HEK)-293T cells. Notably, the Arg-rich domains in RNA-binding proteins are densely modified by methylation and phosphorylation compared with the remainder of the proteome, with methylation and phosphorylation favoring RSRS motifs. Although they favor a common motif, analysis of combinatorial PTMs within RSRS motifs indicates that phosphorylation and methylation do not often co-occur, suggesting that they may functionally oppose one another. Furthermore, we show that phosphorylation may modify interactions between Arg-rich proteins, as serine-arginine splicing factor 2 (SRSF2) has a stronger association with U1-70K and LUC7L3 upon dephosphorylation. Collectively, these findings suggest that the level of PTMs within Arg-rich domains may be among the highest in the proteome and a possible unexplored regulator of RNA-binding protein interactions.
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5
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Ultra-deep sequencing reveals pre-mRNA splicing as a sequence driven high-fidelity process. PLoS One 2019; 14:e0223132. [PMID: 31581208 PMCID: PMC6776343 DOI: 10.1371/journal.pone.0223132] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2019] [Accepted: 09/13/2019] [Indexed: 11/19/2022] Open
Abstract
Alternative splicing diversifies mRNA transcripts in human cells. While the spliceosome pairs exons with a high degree of accuracy, the rates of rare aberrant and non-canonical pre-mRNA splicing have not been evaluated at the nucleotide level to determine the quantity and identity of these events across splice junctions. Using ultra-deep sequencing the frequency of aberrant and non-canonical splicing events for three splice junctions flanking exon 7 of SMN1 were determined at single nucleotide resolution. After correction for background noise introduced by PCR amplification and sequencing steps, pre-mRNA splicing was shown to maintain a low overall rate of aberrant and non-canonically spliced events. Several previously unannotated splicing events across 3 exon|intron junctions in SMN1 were identified. Mutations within SMN exon 7 were shown to affect splicing fidelity by modulating RNA secondary structures, by altering the binding site of regulatory proteins and by changing the 5’ splice site strength. Mutations also create a truncated SMN1 exon 7 through the introduction of a de novo non-canonical 5’ splice site. The results from the ultra-deep sequencing approach highlight the impressive fidelity of pre-mRNA splicing and demonstrate that the immediate sequence context around splice sites is the main driving force behind non-canonical splice site pairing.
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6
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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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7
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Valdés J, Ortuño-Pineda C, Saucedo-Cárdenas O, Mendoza-Figueroa MS. Unexplored Molecular Features of the Entamoeba histolytica RNA Lariat Debranching Enzyme Dbr 1 Expression Profile. Front Cell Infect Microbiol 2018; 8:228. [PMID: 30023353 PMCID: PMC6039765 DOI: 10.3389/fcimb.2018.00228] [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] [Received: 03/25/2018] [Accepted: 06/18/2018] [Indexed: 11/25/2022] Open
Abstract
The RNA lariat debranching enzyme (Dbr1) has different functions in RNA metabolism, such as hydrolyzing the 2′-5′ linkage in intron lariats, positively influencing Ty1 and HIV-1 retrotransposition, and modulating snRNP recycling during splicing reactions. It seems that Dbr1 is one of the major players in RNA turnover. It is remarkable that of all the studies carried out to date with Dbr1, to our knowledge, none of them have evaluated the expression profile of the endogenous Dbr1 gene. In this work, we describe, for the first time, that Entamoeba histolytica EhDbr1 mRNA has a very short half-life (less than 30 min) and encodes a very stable protein that is present until trophozoite cultures die. We also show that the EhDbr1 protein is present in the nuclear periphery on the cytoplasmic basal side, contrary to the localization of human Dbr1. Comparing these results with previous hypotheses and with results from different organisms suggests that Dbr1 gene expression is finely tuned and conserved across eukaryotes. Experiments describing the aspects of Dbr1 gene expression and Dbr1 mRNA turnover as well as other functions of the protein need to be performed. Particularly, a special emphasis is needed on the protozoan parasite E. histolytica, the causative agent of amoebiasis, since even though it is a unicellular organism, it is an intron-rich eukaryote whose intron lariats seem to be open to avoid intron lariat accumulation and to process them in non-coding RNAs that might be involved in its virulence.
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Affiliation(s)
- Jesús Valdés
- Departamento de Bioquímica, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Mexico City, Mexico
| | - Carlos Ortuño-Pineda
- Unidad Académica de Ciencias Químico Biológicas, Universidad Autónoma de Guerrero, Chilpancingo, Mexico
| | - Odila Saucedo-Cárdenas
- Histología, Facultad de Medicina, Universidad Autónoma de Nuevo León, San Nicolás de los Garza, Mexico.,División de Genética, Centro de Investigación Biomédica del Noreste, Instituto Mexicano del Seguro Social, Monterrey, Mexico
| | - María S Mendoza-Figueroa
- Departamento de Bioquímica, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Mexico City, Mexico.,Departamento de Atención a la Salud, Universidad Autónoma Metropolitana-Xochimilco, Mexico City, Mexico
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8
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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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9
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Hálová M, Gahura O, Převorovský M, Cit Z, Novotný M, Valentová A, Abrhámová K, Půta F, Folk P. Nineteen complex-related factor Prp45 is required for the early stages of cotranscriptional spliceosome assembly. RNA (NEW YORK, N.Y.) 2017; 23:1512-1524. [PMID: 28701519 PMCID: PMC5602110 DOI: 10.1261/rna.061986.117] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2017] [Accepted: 06/21/2017] [Indexed: 05/22/2023]
Abstract
Splicing in S. cerevisiae has been shown to proceed cotranscriptionally, but the nature of the coupling remains a subject of debate. Here, we examine the effect of nineteen complex-related splicing factor Prp45 (a homolog of SNW1/SKIP) on cotranscriptional splicing. RNA-sequencing and RT-qPCR showed elevated pre-mRNA levels but only limited reduction of spliced mRNAs in cells expressing C-terminally truncated Prp45, Prp45(1-169). Assays with a series of reporters containing the AMA1 intron with regulatable splicing confirmed decreased splicing efficiency and showed the leakage of unspliced RNAs in prp45(1-169) cells. We also measured pre-mRNA accumulation of the meiotic MER2 gene, which depends on the expression of Mer1 factor for splicing. prp45(1-169) cells accumulated approximately threefold higher levels of MER2 pre-mRNA than WT cells only when splicing was induced. To monitor cotranscriptional splicing, we determined the presence of early spliceosome assembly factors and snRNP complexes along the ECM33 and ACT1 genes. We found that prp45(1-169) hampered the cotranscriptional recruitment of U2 and, to a larger extent, U5 and NTC, while the U1 profile was unaffected. The recruitment of Prp45(1-169) was impaired similarly to U5 snRNP and NTC. Our results imply that Prp45 is required for timely formation of complex A, prior to stable physical association of U5/NTC with the emerging pre-mRNA substrate. We suggest that Prp45 facilitates conformational rearrangements and/or contacts that couple U1 snRNP-recognition to downstream assembly events.
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Affiliation(s)
- Martina Hálová
- Department of Cell Biology, Faculty of Science, Charles University, 128 00 Prague, Czech Republic
| | - Ondřej Gahura
- Department of Cell Biology, Faculty of Science, Charles University, 128 00 Prague, Czech Republic
| | - Martin Převorovský
- Department of Cell Biology, Faculty of Science, Charles University, 128 00 Prague, Czech Republic
| | - Zdeněk Cit
- Department of Cell Biology, Faculty of Science, Charles University, 128 00 Prague, Czech Republic
| | - Marian Novotný
- Department of Cell Biology, Faculty of Science, Charles University, 128 00 Prague, Czech Republic
| | - Anna Valentová
- Department of Cell Biology, Faculty of Science, Charles University, 128 00 Prague, Czech Republic
| | - Kateřina Abrhámová
- Department of Cell Biology, Faculty of Science, Charles University, 128 00 Prague, Czech Republic
| | - František Půta
- Department of Cell Biology, Faculty of Science, Charles University, 128 00 Prague, Czech Republic
| | - Petr Folk
- Department of Cell Biology, Faculty of Science, Charles University, 128 00 Prague, Czech Republic
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10
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Tseng CK, Chung CS, Chen HC, Cheng SC. A central role of Cwc25 in spliceosome dynamics during the catalytic phase of pre-mRNA splicing. RNA (NEW YORK, N.Y.) 2017; 23:546-556. [PMID: 28057857 PMCID: PMC5340917 DOI: 10.1261/rna.059204.116] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/16/2016] [Accepted: 01/03/2017] [Indexed: 05/22/2023]
Abstract
Splicing of precursor mRNA occurs via two consecutive steps of transesterification reaction; both require ATP and several proteins. Despite the energy requirement in the catalytic phase, incubation of the purified spliceosome under proper ionic conditions can elicit competitive reversible transesterification, debranching, and spliced-exon-reopening reactions without the necessity for ATP or other factors, suggesting that small changes in the conformational state of the spliceosome can lead to disparate chemical consequences for the substrate. We show here that Cwc25 plays a central role in modulating the conformational state of the catalytic spliceosome during normal splicing reactions. Cwc25 binds tightly to the spliceosome after the reaction and is then removed from the spliceosome, which normally requires DExD/H-box protein Prp16 and ATP hydrolysis, to allow the occurrence of the second reaction. When deprived of Cwc25, the purified first-step spliceosome catalyzes both forward and reverse splicing reactions under normal splicing conditions without requiring energy. Both reactions are inhibited when Cwc25 is added back, presumably due to the stabilization of first-step conformation. Prp16 is dispensable for the second reaction when splicing is carried out under conditions that destabilize Cwc25. We also show that the purified precatalytic spliceosome can catalyze two steps of the reaction at a low efficiency without requiring Cwc25, Slu7, or Prp18 when incubated under proper conditions. Our study reveals conformational modulation of the spliceosome by Cwc25 and Prp16 in stabilization and destabilization of first-step conformation, respectively, to facilitate the splicing process.
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Affiliation(s)
- Chi-Kang Tseng
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan 115, Republic of China
| | - Che-Sheng Chung
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan 115, Republic of China
| | - Hsin-Chou Chen
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan 115, Republic of China
| | - Soo-Chen Cheng
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan 115, Republic of China
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11
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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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12
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Absmeier E, Santos KF, Wahl MC. Functions and regulation of the Brr2 RNA helicase during splicing. Cell Cycle 2016; 15:3362-3377. [PMID: 27792457 DOI: 10.1080/15384101.2016.1249549] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Pre-mRNA splicing entails the stepwise assembly of an inactive spliceosome, its catalytic activation, splicing catalysis and spliceosome disassembly. Transitions in this reaction cycle are accompanied by compositional and conformational rearrangements of the underlying RNA-protein interaction networks, which are driven and controlled by 8 conserved superfamily 2 RNA helicases. The Ski2-like helicase, Brr2, provides the key remodeling activity during spliceosome activation and is additionally implicated in the catalytic and disassembly phases of splicing, indicating that Brr2 needs to be tightly regulated during splicing. Recent structural and functional analyses have begun to unravel how Brr2 regulation is established via multiple layers of intra- and inter-molecular mechanisms. Brr2 has an unusual structure, including a long N-terminal region and a catalytically inactive C-terminal helicase cassette, which can auto-inhibit and auto-activate the enzyme, respectively. Both elements are essential, also serve as protein-protein interaction devices and the N-terminal region is required for stable Brr2 association with the tri-snRNP, tri-snRNP stability and retention of U5 and U6 snRNAs during spliceosome activation in vivo. Furthermore, a C-terminal region of the Prp8 protein, comprising consecutive RNase H-like and Jab1/MPN-like domains, can both up- and down-regulate Brr2 activity. Biochemical studies revealed an intricate cross-talk among the various cis- and trans-regulatory mechanisms. Comparison of isolated Brr2 to electron cryo-microscopic structures of yeast and human U4/U6•U5 tri-snRNPs and spliceosomes indicates how some of the regulatory elements exert their functions during splicing. The various modulatory mechanisms acting on Brr2 might be exploited to enhance splicing fidelity and to regulate alternative splicing.
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Affiliation(s)
- Eva Absmeier
- a Freie Universität Berlin, Laboratory of Structural Biochemistry , Berlin , Germany
| | - Karine F Santos
- a Freie Universität Berlin, Laboratory of Structural Biochemistry , Berlin , Germany
| | - Markus C Wahl
- a Freie Universität Berlin, Laboratory of Structural Biochemistry , Berlin , Germany.,b Helmholtz-Zentrum Berlin für Materialien und Energie, Macromolecular Crystallography , Berlin , Germany
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13
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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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14
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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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15
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Rose AM, Bhattacharya SS. Variant haploinsufficiency and phenotypic non-penetrance in PRPF31-associated retinitis pigmentosa. Clin Genet 2016; 90:118-26. [PMID: 26853529 DOI: 10.1111/cge.12758] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2015] [Revised: 02/02/2016] [Accepted: 02/03/2016] [Indexed: 11/30/2022]
Abstract
Retinitis pigmentosa (RP) is a genetically heterogenous group of inherited disorders, characterized by death of the retinal photoreceptor cells, leading to progressive visual impairment. One form of RP is caused by mutations in the ubiquitously expressed splicing factor, PRPF31, this form being known as RP11. An intriguing feature of RP11 is the presence of non-penetrance, which has been observed in the majority of PRPF31 mutation-carrying families. In contrast to variable expressivity, which is highly pervasive, true non-penetrance is a very rare phenomenon in Mendelian disorders. In this article, the molecular mechanisms underlying phenotypic non-penetrance in RP11 are explored. It is an elegant example of how our understanding of monogenic disorders has evolved from studying only the disease gene, to considering a mutation on the genetic background of the individual - the logical evolution in this genomic era.
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Affiliation(s)
- A M Rose
- Department of Genetics, UCL Institute of Ophthalmology, London, UK
| | - S S Bhattacharya
- Department of Genetics, UCL Institute of Ophthalmology, London, UK
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16
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Rodgers ML, Tretbar US, Dehaven A, Alwan AA, Luo G, Mast HM, Hoskins AA. Conformational dynamics of stem II of the U2 snRNA. RNA (NEW YORK, N.Y.) 2016; 22:225-36. [PMID: 26631165 PMCID: PMC4712673 DOI: 10.1261/rna.052233.115] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2015] [Accepted: 10/27/2015] [Indexed: 05/25/2023]
Abstract
The spliceosome undergoes dramatic changes in both small nuclear RNA (snRNA) composition and structure during assembly and pre-mRNA splicing. It has been previously proposed that the U2 snRNA adopts two conformations within the stem II region: stem IIa or stem IIc. Dynamic rearrangement of stem IIa into IIc and vice versa is necessary for proper progression of the spliceosome through assembly and catalysis. How this conformational transition is regulated is unclear; although, proteins such as Cus2p and the helicase Prp5p have been implicated in this process. We have used single-molecule Förster resonance energy transfer (smFRET) to study U2 stem II toggling between stem IIa and IIc. Structural interconversion of the RNA was spontaneous and did not require the presence of a helicase; however, both Mg(2+) and Cus2p promote formation of stem IIa. Destabilization of stem IIa by a G53A mutation in the RNA promotes stem IIc formation and inhibits conformational switching of the RNA by both Mg(2+) and Cus2p. Transitioning to stem IIa can be restored using Cus2p mutations that suppress G53A phenotypes in vivo. We propose that during spliceosome assembly, Cus2p and Mg(2+) may work together to promote stem IIa formation. During catalysis the spliceosome could then toggle stem II with the aid of Mg(2+) or with the use of functionally equivalent protein interactions. As noted in previous studies, the Mg(2+) toggling we observe parallels previous observations of U2/U6 and Prp8p RNase H domain Mg(2+)-dependent conformational changes. Together these data suggest that multiple components of the spliceosome may have evolved to switch between conformations corresponding to open or closed active sites with the aid of metal and protein cofactors.
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Affiliation(s)
- Margaret L Rodgers
- Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA
| | - U Sandy Tretbar
- Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA
| | - Alexander Dehaven
- Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA
| | - Amir A Alwan
- Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA
| | - George Luo
- Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA
| | - Hannah M Mast
- Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA
| | - Aaron A Hoskins
- Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA
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17
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Papasaikas P, Valcárcel J. The Spliceosome: The Ultimate RNA Chaperone and Sculptor. Trends Biochem Sci 2015; 41:33-45. [PMID: 26682498 DOI: 10.1016/j.tibs.2015.11.003] [Citation(s) in RCA: 171] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2015] [Revised: 11/02/2015] [Accepted: 11/06/2015] [Indexed: 01/08/2023]
Abstract
The spliceosome, one of the most complex machineries of eukaryotic cells, removes intronic sequences from primary transcripts to generate functional messenger and long noncoding RNAs (lncRNA). Genetic, biochemical, and structural data reveal that the spliceosome is an RNA-based enzyme. Striking mechanistic and structural similarities strongly argue that pre-mRNA introns originated from self-catalytic group II ribozymes. However, in the spliceosome, protein components organize and activate the catalytic-site RNAs, and recognize and pair together splice sites at intron boundaries. The spliceosome is a dynamic, reversible, and flexible machine that chaperones small nuclear (sn) RNAs and a variety of pre-mRNA sequences into conformations that enable intron removal. This malleability likely contributes to the regulation of alternative splicing, a prevalent process contributing to cell differentiation, homeostasis, and disease.
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Affiliation(s)
- Panagiotis Papasaikas
- Centre de Regulació Genòmica, The Barcelona Institute of Science and Technology, Dr. Aiguader 88, 08003 Barcelona, Spain; Universitat Pompeu-Fabra, Dr. Aiguader 88, 08003 Barcelona, Spain
| | - Juan Valcárcel
- Centre de Regulació Genòmica, The Barcelona Institute of Science and Technology, Dr. Aiguader 88, 08003 Barcelona, Spain; Universitat Pompeu-Fabra, Dr. Aiguader 88, 08003 Barcelona, Spain; ICREA, Passeig Lluis Companys 23, 08010 Barcelona, Spain.
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18
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Liu S, Mozaffari-Jovin S, Wollenhaupt J, Santos KF, Theuser M, Dunin-Horkawicz S, Fabrizio P, Bujnicki JM, Lührmann R, Wahl MC. A composite double-/single-stranded RNA-binding region in protein Prp3 supports tri-snRNP stability and splicing. eLife 2015; 4:e07320. [PMID: 26161500 PMCID: PMC4520091 DOI: 10.7554/elife.07320] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2015] [Accepted: 07/09/2015] [Indexed: 12/05/2022] Open
Abstract
Prp3 is an essential U4/U6 di-snRNP-associated protein whose functions and molecular mechanisms in pre-mRNA splicing are presently poorly understood. We show by structural and biochemical analyses that Prp3 contains a bipartite U4/U6 di-snRNA-binding region comprising an expanded ferredoxin-like fold, which recognizes a 3′-overhang of U6 snRNA, and a preceding peptide, which binds U4/U6 stem II. Phylogenetic analyses revealed that the single-stranded RNA-binding domain is exclusively found in Prp3 orthologs, thus qualifying as a spliceosome-specific RNA interaction module. The composite double-stranded/single-stranded RNA-binding region assembles cooperatively with Snu13 and Prp31 on U4/U6 di-snRNAs and inhibits Brr2-mediated U4/U6 di-snRNA unwinding in vitro. RNP-disrupting mutations in Prp3 lead to U4/U6•U5 tri-snRNP assembly and splicing defects in vivo. Our results reveal how Prp3 acts as an important bridge between U4/U6 and U5 in the tri-snRNP and comparison with a Prp24-U6 snRNA recycling complex suggests how Prp3 may be involved in U4/U6 reassembly after splicing. DOI:http://dx.doi.org/10.7554/eLife.07320.001 Proteins are built following instructions contained within the DNA of gene sequences. This genetic information is copied into short-lived molecules, called messenger RNAs (or mRNAs), which move away from the DNA and are then decoded by the molecular machines that build proteins. However, mRNA sequences often have to be edited before they are used. Another molecular machine, called a spliceosome, carries out some of this editing. A spliceosome is formed from a number of smaller subunits, including three RNA-protein particles that each contain one RNA molecule (called U1, U2 and U5), and one particle that contains two RNA molecules (called U4 and U6). These subunits must assemble around an unedited mRNA in a particular order so that the spliceosome can work correctly. Once the mRNA has been edited, and the spliceosome has performed its job, these complexes need to disassemble so that they are ready to be reassembled around a new mRNA molecule. A protein called Prp3 is known to be involved in these assembly, disassembly and reassembly steps. However, it is unclear how this protein performs these activities. Liu et al. have now used structural biology and biochemical techniques to determine the three-dimensional structure of Prp3, and have shown that this protein has a “two-part” binding site that binds to the RNA molecules in the U4/U6 subunit of the spliceosome. Further analyses revealed that one of these features is only found in Prp3 and not in other types of RNA-binding proteins. Together with previous work, Liu et al. also reveal that Prp3 can serve as a ‘bridge’ between the U4/U6 and U5 subunits of the spliceosome, and suggest how these features allow the two subunits to group together before they are incorporated into a spliceosome. Notably, certain mutations in the gene for the Prp3 protein lead to a human eye disease called retinitis pigmentosa. In the future it will be important to investigate if the above activities are affected in the mutant variants of the Prp3 protein. DOI:http://dx.doi.org/10.7554/eLife.07320.002
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Affiliation(s)
- Sunbin Liu
- Laboratory of Structural Biochemistry, Freie Universität Berlin, Berlin, Germany
| | - Sina Mozaffari-Jovin
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Jan Wollenhaupt
- Laboratory of Structural Biochemistry, Freie Universität Berlin, Berlin, Germany
| | - Karine F Santos
- Laboratory of Structural Biochemistry, Freie Universität Berlin, Berlin, Germany
| | - Matthias Theuser
- Laboratory of Structural Biochemistry, Freie Universität Berlin, Berlin, Germany
| | - Stanislaw Dunin-Horkawicz
- Laboratory of Bioinformatics and Protein Engineering, International Institute of Molecular and Cell Biology, Warsaw, Poland
| | - Patrizia Fabrizio
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Janusz M Bujnicki
- Laboratory of Bioinformatics and Protein Engineering, International Institute of Molecular and Cell Biology, Warsaw, Poland
| | - Reinhard Lührmann
- Department of Cellular Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Markus C Wahl
- Laboratory of Structural Biochemistry, Freie Universität Berlin, Berlin, Germany
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19
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Gautam A, Grainger RJ, Vilardell J, Barrass JD, Beggs JD. Cwc21p promotes the second step conformation of the spliceosome and modulates 3' splice site selection. Nucleic Acids Res 2015; 43:3309-17. [PMID: 25740649 PMCID: PMC4381068 DOI: 10.1093/nar/gkv159] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2015] [Accepted: 02/18/2015] [Indexed: 12/20/2022] Open
Abstract
Pre-mRNA splicing involves two transesterification steps catalyzed by the spliceosome. How RNA substrates are positioned in each step and the molecular rearrangements involved, remain obscure. Here, we show that mutations in PRP16, PRP8, SNU114 and the U5 snRNA that affect this process interact genetically with CWC21, that encodes the yeast orthologue of the human SR protein, SRm300/SRRM2. Our microarray analysis shows changes in 3′ splice site selection at elevated temperature in a subset of introns in cwc21Δ cells. Considering all the available data, we propose a role for Cwc21p positioning the 3′ splice site at the transition to the second step conformation of the spliceosome, mediated through its interactions with the U5 snRNP. This suggests a mechanism whereby SRm300/SRRM2, might influence splice site selection in human cells.
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MESH Headings
- Adenosine Triphosphatases/chemistry
- Adenosine Triphosphatases/genetics
- Adenosine Triphosphatases/metabolism
- Alternative Splicing
- Amino Acid Sequence
- Carrier Proteins/chemistry
- Carrier Proteins/genetics
- Carrier Proteins/metabolism
- Gene Deletion
- Genes, Fungal
- Humans
- Molecular Sequence Data
- Nucleic Acid Conformation
- Protein Conformation
- RNA Helicases/chemistry
- RNA Helicases/genetics
- RNA Helicases/metabolism
- RNA Precursors/chemistry
- RNA Precursors/genetics
- RNA Precursors/metabolism
- RNA Splice Sites
- RNA Splicing
- RNA Splicing Factors
- RNA, Fungal/chemistry
- RNA, Fungal/genetics
- RNA, Fungal/metabolism
- RNA-Binding Proteins/chemistry
- RNA-Binding Proteins/genetics
- RNA-Binding Proteins/metabolism
- Ribonucleoprotein, U4-U6 Small Nuclear/chemistry
- Ribonucleoprotein, U4-U6 Small Nuclear/genetics
- Ribonucleoprotein, U4-U6 Small Nuclear/metabolism
- Ribonucleoprotein, U5 Small Nuclear/chemistry
- Ribonucleoprotein, U5 Small Nuclear/genetics
- Ribonucleoprotein, U5 Small Nuclear/metabolism
- Saccharomyces cerevisiae/genetics
- Saccharomyces cerevisiae/metabolism
- Saccharomyces cerevisiae Proteins/chemistry
- Saccharomyces cerevisiae Proteins/genetics
- Saccharomyces cerevisiae Proteins/metabolism
- Spliceosomes/chemistry
- Spliceosomes/genetics
- Spliceosomes/metabolism
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Affiliation(s)
- Amit Gautam
- Wellcome Trust Centre for Cell Biology, University of Edinburgh, King's Buildings, Mayfield Road, Edinburgh, EH9 3BF, UK
| | - Richard J Grainger
- Wellcome Trust Centre for Cell Biology, University of Edinburgh, King's Buildings, Mayfield Road, Edinburgh, EH9 3BF, UK
| | - J Vilardell
- Department of Molecular Genomics, Institute of Molecular Biology of Barcelona (IBMB), 08028 Barcelona, Spain Institució Catalana de Recerca i Estudis Avançats (ICREA), 08010 Barcelona, Spain
| | - J David Barrass
- Wellcome Trust Centre for Cell Biology, University of Edinburgh, King's Buildings, Mayfield Road, Edinburgh, EH9 3BF, UK
| | - Jean D Beggs
- Wellcome Trust Centre for Cell Biology, University of Edinburgh, King's Buildings, Mayfield Road, Edinburgh, EH9 3BF, UK
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20
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Kannan R, Helston RM, Dannebaum RO, Baumann P. Diverse mechanisms for spliceosome-mediated 3' end processing of telomerase RNA. Nat Commun 2015; 6:6104. [PMID: 25598145 PMCID: PMC4299874 DOI: 10.1038/ncomms7104] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2014] [Accepted: 12/15/2014] [Indexed: 11/13/2022] Open
Abstract
The 3′ end of Schizosaccharomyces pombe telomerase RNA (SpTER1) is generated by spliceosomal cleavage, a reaction that corresponds to the first step of splicing. The observation that the spliceosome functions in 3′ end processing raised questions about the evolutionary origin and conservation of this mechanism. We now present data in support of spliceosomes generating 3′ ends of telomerase RNAs in other fungi. Strikingly, the mechanistic basis for restricting spliceosomal splicing to the first transesterification reaction differs substantially among species. Unlike S. pombe, two other fission yeasts rely on hyperstabilization of the U6 snRNA—5′ splice site interaction to impede the 2nd step of splicing. In contrast, a non-canonical 5′ splice site blocks the second transesterification reaction in Aspergillus species. These results demonstrate a conserved role for spliceosomes functioning in 3′ end processing. Divergent mechanisms of uncoupling the two steps of splicing argue for multiple origins of this pathway. In fission yeast, the telomerase RNA (TER) is produced through spliceosomal cleavage. Here, Kannan et al. find that spliceosome-generated 3′ ends also occurs in other fungal TERs using distinct molecular mechanisms, suggesting multiple origins for this type of TER maturation pathway.
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Affiliation(s)
- Ram Kannan
- 1] Stowers Institute for Medical Research, Kansas City, Missouri 64110, USA [2] Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, Kansas 66160, USA
| | - Rachel M Helston
- Stowers Institute for Medical Research, Kansas City, Missouri 64110, USA
| | | | - Peter Baumann
- 1] Stowers Institute for Medical Research, Kansas City, Missouri 64110, USA [2] Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, Kansas 66160, USA [3] Howard Hughes Medical Institute, Kansas City, Missouri 64110, USA
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21
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Wickramasinghe VO, Gonzàlez-Porta M, Perera D, Bartolozzi AR, Sibley CR, Hallegger M, Ule J, Marioni JC, Venkitaraman AR. Regulation of constitutive and alternative mRNA splicing across the human transcriptome by PRPF8 is determined by 5' splice site strength. Genome Biol 2015; 16:201. [PMID: 26392272 PMCID: PMC4578845 DOI: 10.1186/s13059-015-0749-3] [Citation(s) in RCA: 73] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2015] [Accepted: 07/27/2015] [Indexed: 02/02/2023] Open
Abstract
BACKGROUND Sequential assembly of the human spliceosome on RNA transcripts regulates splicing across the human transcriptome. The core spliceosome component PRPF8 is essential for spliceosome assembly through its participation in ribonucleoprotein (RNP) complexes for splice-site recognition, branch-point formation and catalysis. PRPF8 deficiency is linked to human diseases like retinitis pigmentosa or myeloid neoplasia, but its genome-wide effects on constitutive and alternative splicing remain unclear. RESULTS Here, we show that alterations in RNA splicing patterns across the human transcriptome that occur in conditions of restricted cellular PRPF8 abundance are defined by the altered splicing of introns with weak 5' splice sites. iCLIP of spliceosome components reveals that PRPF8 depletion decreases RNP complex formation at most splice sites in exon-intron junctions throughout the genome. However, impaired splicing affects only a subset of human transcripts, enriched for mitotic cell cycle factors, leading to mitotic arrest. Preferentially retained introns and differentially used exons in the affected genes contain weak 5' splice sites, but are otherwise indistinguishable from adjacent spliced introns. Experimental enhancement of splice-site strength in mini-gene constructs overcomes the effects of PRPF8 depletion on the kinetics and fidelity of splicing during transcription. CONCLUSIONS Competition for PRPF8 availability alters the transcription-coupled splicing of RNAs in which weak 5' splice sites predominate, enabling diversification of human gene expression during biological processes like mitosis. Our findings exemplify the regulatory potential of changes in the core spliceosome machinery, which may be relevant to slow-onset human genetic diseases linked to PRPF8 deficiency.
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Affiliation(s)
- Vihandha O. Wickramasinghe
- The Medical Research Council Cancer Unit, University of Cambridge, Cambridge Biomedical Campus, Box 197, Cambridge, CB2 0XZ UK
| | - Mar Gonzàlez-Porta
- European Molecular Biology Laboratory - European Bioinformatics Institute (EMBL-EBI), Hinxton, UK
| | - David Perera
- The Medical Research Council Cancer Unit, University of Cambridge, Cambridge Biomedical Campus, Box 197, Cambridge, CB2 0XZ UK
| | - Arthur R. Bartolozzi
- The Medical Research Council Cancer Unit, University of Cambridge, Cambridge Biomedical Campus, Box 197, Cambridge, CB2 0XZ UK
| | - Christopher R. Sibley
- Department of Molecular Neuroscience, UCL Institute of Neurology, Queen Square, London, WC1N 3BG UK
| | - Martina Hallegger
- Department of Molecular Neuroscience, UCL Institute of Neurology, Queen Square, London, WC1N 3BG UK
| | - Jernej Ule
- Department of Molecular Neuroscience, UCL Institute of Neurology, Queen Square, London, WC1N 3BG UK
| | - John C. Marioni
- European Molecular Biology Laboratory - European Bioinformatics Institute (EMBL-EBI), Hinxton, UK
| | - Ashok R. Venkitaraman
- The Medical Research Council Cancer Unit, University of Cambridge, Cambridge Biomedical Campus, Box 197, Cambridge, CB2 0XZ UK
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22
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Fica SM, Mefford MA, Piccirilli JA, Staley JP. Evidence for a group II intron-like catalytic triplex in the spliceosome. Nat Struct Mol Biol 2014; 21:464-471. [PMID: 24747940 PMCID: PMC4257784 DOI: 10.1038/nsmb.2815] [Citation(s) in RCA: 84] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2013] [Accepted: 03/27/2014] [Indexed: 01/04/2023]
Abstract
To catalyze pre-mRNA splicing, U6 small nuclear RNA positions two metals that interact directly with the scissile phosphates. U6 metal ligands correspond stereospecifically to metal ligands within the catalytic domain V of a group II self-splicing intron. Domain V ligands are organized by base-triple interactions, which also juxtapose the 3' splice site with the catalytic metals. However, in the spliceosome, the mechanism for organizing catalytic metals and recruiting the substrate has remained unclear. Here we show by genetics, cross-linking and biochemistry in yeast that analogous triples form in U6 and promote catalytic-metal binding and both chemical steps of splicing. Because the triples include an element that defines the 5' splice site, they also provide a mechanism for juxtaposing the pre-mRNA substrate with the catalytic metals. Our data indicate that U6 adopts a group II intron-like tertiary conformation to catalyze splicing.
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Affiliation(s)
- Sebastian M Fica
- Graduate Program in Cell and Molecular Biology, The University of Chicago, Chicago IL.,Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago IL
| | - Melissa A Mefford
- Committee on Genetics Genomics and Systems Biology, The University of Chicago, Chicago, IL
| | - Joseph A Piccirilli
- Department of Chemistry, The University of Chicago, Chicago IL.,Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL
| | - Jonathan P Staley
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago IL
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23
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Valadkhan S. The role of snRNAs in spliceosomal catalysis. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2014; 120:195-228. [PMID: 24156945 DOI: 10.1016/b978-0-12-381286-5.00006-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/15/2023]
Abstract
The spliceosomes, large ribonucleoprotein (RNP) assemblies that remove the intervening sequences from pre-mRNAs, contain a large number of proteins and five small nuclear RNAs (snRNAs). One snRNA, U6, contains highly conserved sequences that are thought to be the functional counterparts of the RNA elements that form the active site of self-splicing group II intron ribozymes. An in vitro-assembled, protein-free complex of U6 with U2, the base-pairing partner in the spliceosomal catalytic core, can catalyze a two-step splicing reaction in the absence of all other spliceosomal factors, suggesting that the two snRNAs may form all or a large share of the spliceosomal active site. On the other hand, several spliceosomal proteins are thought to help in the formation of functionally required RNA-RNA interactions in the catalytic core. Whether they also contribute functional groups to the spliceosomal active site, and thus whether the spliceosomes are RNA or RNP enzymes remain uncertain.
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Affiliation(s)
- Saba Valadkhan
- Department of Biochemistry, Case Western Reserve University, Cleveland, Ohio, USA
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24
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Wlodaver AM, Staley JP. The DExD/H-box ATPase Prp2p destabilizes and proofreads the catalytic RNA core of the spliceosome. RNA (NEW YORK, N.Y.) 2014; 20:282-94. [PMID: 24442613 PMCID: PMC3923124 DOI: 10.1261/rna.042598.113] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2013] [Accepted: 10/30/2013] [Indexed: 05/25/2023]
Abstract
After undergoing massive RNA and protein rearrangements during assembly, the spliceosome undergoes a final, more subtle, ATP-dependent rearrangement that is essential for catalysis. This rearrangement requires the DEAH-box protein Prp2p, an RNA-dependent ATPase. Prp2p has been implicated in destabilizing interactions between the spliceosome and the protein complexes SF3 and RES, but a role for Prp2p in destabilizing RNA-RNA interactions has not been explored. Using directed molecular genetics in budding yeast, we have found that a cold-sensitive prp2 mutation is suppressed not only by mutations in SF3 and RES components but also by a range of mutations that disrupt the spliceosomal catalytic core element U2/U6 helix I, which is implicated in juxtaposing the 5' splice site and branch site and in positioning metal ions for catalysis within the context of a putative catalytic triplex; indeed, mutations in this putative catalytic triplex also suppressed a prp2 mutation. Remarkably, we also found that prp2 mutations rescue lethal mutations in U2/U6 helix I. These data provide evidence that RNA elements that comprise the catalytic core are already formed at the Prp2p stage and that Prp2p destabilizes these elements, directly or indirectly, both to proofread spliceosome activation and to promote reconfiguration of the spliceosome to a fully competent, catalytic conformation.
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25
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Chen W, Moore MJ. The spliceosome: disorder and dynamics defined. Curr Opin Struct Biol 2014; 24:141-9. [PMID: 24530854 DOI: 10.1016/j.sbi.2014.01.009] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2013] [Revised: 01/07/2014] [Accepted: 01/14/2014] [Indexed: 01/02/2023]
Abstract
Among the many macromolecular machines involved in eukaryotic gene expression, the spliceosome remains one of the most challenging for structural biologists. Defining features of this highly complex apparatus are its excessive number of individual parts, many of which have been evolutionarily selected for regions of structural disorder, and the remarkable compositional and conformation dynamics it must undertake to complete each round of splicing. Here we review recent advances in our understanding of spliceosome structural dynamics stemming from bioinformatics, deep sequencing, high throughput methods for determining protein-protein, protein-RNA and RNA-RNA interaction dynamics, single molecule microscopy and more traditional structural analyses. Together, these tools are rapidly changing our structural appreciation of this remarkably dynamic machine.
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Affiliation(s)
- Weijun Chen
- Howard Hughes Medical Institute, Department of Biochemistry and Molecular Pharmacology, RNA and Neuro Therapeutics Institutes, University of Massachusetts Medical School, Worcester, MA 01655, USA
| | - Melissa J Moore
- Howard Hughes Medical Institute, Department of Biochemistry and Molecular Pharmacology, RNA and Neuro Therapeutics Institutes, University of Massachusetts Medical School, Worcester, MA 01655, USA.
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26
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Zhang ZM, Yang F, Zhang J, Tang Q, Li J, Gu J, Zhou J, Xu YZ. Crystal structure of Prp5p reveals interdomain interactions that impact spliceosome assembly. Cell Rep 2013; 5:1269-78. [PMID: 24290758 DOI: 10.1016/j.celrep.2013.10.047] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2013] [Revised: 09/30/2013] [Accepted: 10/29/2013] [Indexed: 01/13/2023] Open
Abstract
The DEAD-box adenosine triphosphatase (ATPase) Prp5p facilitates U2 small nuclear ribonucleoprotein particle (snRNP) binding to the intron branch site region during spliceosome assembly. We present crystal structures of S. cerevisiae Prp5p alone and in complex with ADP at 2.12 Å and 1.95 Å resolution. The three-dimensional packing of Prp5p subdomains differs strikingly from that so far observed in other DEAD-box proteins: two RecA-like subdomains adopt an "open state" conformation stabilized by extensive interactions involving sequences that flank the two subdomains. This conformation is distinct from that required for ATP hydrolysis. Consistent with this, Prp5p mutations that destabilize interdomain interactions exhibited increased ATPase activity in vitro and inhibited splicing of suboptimal branch site substrates in vivo, whereas restoration of interdomain interactions reversed these effects. We conclude that the Prp5p open state conformation is biologically relevant and that disruption of the interdomain interaction facilitates a large-scale conformational change of Prp5p during U2 snRNP-branch site recognition.
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Affiliation(s)
- Zhi-Min Zhang
- State Key Laboratory of Bio-organic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, China
| | - Fei Yang
- Key Laboratory of Insect Developmental and Evolutionary Biology, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China
| | - Jinru Zhang
- State Key Laboratory of Bio-organic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, China
| | - Qing Tang
- Key Laboratory of Insect Developmental and Evolutionary Biology, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China
| | - Jie Li
- State Key Laboratory of Bio-organic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, China
| | - Jing Gu
- Key Laboratory of Insect Developmental and Evolutionary Biology, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China
| | - Jiahai Zhou
- State Key Laboratory of Bio-organic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, China.
| | - Yong-Zhen Xu
- Key Laboratory of Insect Developmental and Evolutionary Biology, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China.
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27
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Ohrt T, Odenwälder P, Dannenberg J, Prior M, Warkocki Z, Schmitzová J, Karaduman R, Gregor I, Enderlein J, Fabrizio P, Lührmann R. Molecular dissection of step 2 catalysis of yeast pre-mRNA splicing investigated in a purified system. RNA (NEW YORK, N.Y.) 2013; 19:902-15. [PMID: 23685439 PMCID: PMC3683925 DOI: 10.1261/rna.039024.113] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2013] [Accepted: 04/08/2013] [Indexed: 05/04/2023]
Abstract
Step 2 catalysis of pre-mRNA splicing entails the excision of the intron and ligation of the 5' and 3' exons. The tasks of the splicing factors Prp16, Slu7, Prp18, and Prp22 in the formation of the step 2 active site of the spliceosome and in exon ligation, and the timing of their recruitment, remain poorly understood. Using a purified yeast in vitro splicing system, we show that only the DEAH-box ATPase Prp16 is required for formation of a functional step 2 active site and for exon ligation. Efficient docking of the 3' splice site (3'SS) to the active site requires only Slu7/Prp18 but not Prp22. Spliceosome remodeling by Prp16 appears to be subtle as only the step 1 factor Cwc25 is dissociated prior to step 2 catalysis, with its release dependent on docking of the 3'SS to the active site and Prp16 action. We show by fluorescence cross-correlation spectroscopy that Slu7/Prp18 and Prp16 bind early to distinct, low-affinity binding sites on the step-1-activated B* spliceosome, which are subsequently converted into high-affinity sites. Our results shed new light on the factor requirements for step 2 catalysis and the dynamics of step 1 and 2 factors during the catalytic steps of splicing.
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Affiliation(s)
- Thomas Ohrt
- Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
| | - Peter Odenwälder
- Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
| | - Julia Dannenberg
- Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
| | - Mira Prior
- III. Physikalisches Institut (Biophysik), University of Göttingen, 37077 Göttingen, Germany
| | - Zbigniew Warkocki
- Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
| | - Jana Schmitzová
- Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
| | - Ramazan Karaduman
- Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
| | - Ingo Gregor
- III. Physikalisches Institut (Biophysik), University of Göttingen, 37077 Göttingen, Germany
| | - Jörg Enderlein
- III. Physikalisches Institut (Biophysik), University of Göttingen, 37077 Göttingen, Germany
| | - Patrizia Fabrizio
- Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
| | - Reinhard Lührmann
- Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany
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28
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Mroczek S, Dziembowski A. U6 RNA biogenesis and disease association. WILEY INTERDISCIPLINARY REVIEWS-RNA 2013; 4:581-92. [PMID: 23776162 DOI: 10.1002/wrna.1181] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2013] [Revised: 05/14/2013] [Accepted: 05/15/2013] [Indexed: 12/15/2022]
Abstract
U6 snRNA is one of five uridine-rich noncoding RNAs that form the major spliceosome complex. Unlike other U-snRNAs, it reveals many distinctive aspects of biogenesis such as transcription by RNA polymerase III, transcript nuclear retention and particular features of transcript ends: monomethylated 5'-guanosine triphosphate as cap structure and a 2',3'-cyclic phosphate moiety (>P) at the 3' termini. U6-snRNA plays a central role in splicing and thus its transcription, maturation, snRNP formation, and recycling are essential for cellular homeostasis. U6 snRNA enters the splicing cycle as part of the tri-U4/U6.U5snRNP complex, and after significant structural arrangements forms the catalytic site of the spliceosome together with U2 snRNA and Prp8. U6 snRNA also contributes to the splicing reaction by coordinating metal cations required for catalysis. Many human diseases are associated with altered splicing processes. Disruptions of the basal splicing machinery can be lethal or lead to severe diseases such as spinal muscular atrophy, amyotrophic lateral sclerosis, or retinitis pigmentosa. Recent studies have identified a new U6 snRNA biogenesis factor Usb1, the absence of which leads to poikiloderma with neutropenia (PN) (OMIM 604173), an autosomal recessive skin disease. Usb1 is an evolutionarily conserved 3'→5' exoribonuclease that is responsible for removing 3'-terminal uridines from U6 snRNA transcripts, which leads to the formation of a 2',3' cyclic phosphate moiety (>P). This maturation step is fundamental for U6 snRNP assembly and recycling. Usb1 represents the first example of a direct association between a spliceosomal U6 snRNA biogenesis factor and human genetic disease.
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Affiliation(s)
- Seweryn Mroczek
- Department of Biophysics, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland
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29
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Chiou NT, Shankarling G, Lynch KW. hnRNP L and hnRNP A1 induce extended U1 snRNA interactions with an exon to repress spliceosome assembly. Mol Cell 2013; 49:972-82. [PMID: 23394998 PMCID: PMC3595347 DOI: 10.1016/j.molcel.2012.12.025] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2012] [Revised: 11/16/2012] [Accepted: 12/20/2012] [Indexed: 11/22/2022]
Abstract
Pre-mRNA splicing is catalyzed through the activity of the spliceosome, a dynamic enzymatic complex. Forcing aberrant interactions within the spliceosome can reduce splicing efficiency and alter splice site choice; however, it is unknown whether such alterations are naturally exploited mechanisms of splicing regulation. Here, we demonstrate that hnRNP L represses CD45 exon 4 by recruiting hnRNP A1 to a sequence upstream of the 5' splice site. Together, hnRNP L and A1 induce extended contacts between the 5' splice site-bound U1 snRNA and neighboring exonic sequences that, in turn, inhibit stable association of U6 snRNA and subsequent catalysis. Importantly, analysis of several exons regulated by hnRNP L shows a clear relationship between the potential for binding of hnRNP A1 and U1 snRNA and the effect of hnRNP L on splicing. Together, our results demonstrate that conformational perturbations within the spliceosome are a naturally occurring and generalizable mechanism for controlling alternative splicing decisions.
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Affiliation(s)
- Ni-Ting Chiou
- Department of Biochemistry and Biophysics, University of Pennsylvania, Perelman School of Medicine, Philadelphia, PA 19104-6059, USA
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30
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Kannan R, Hartnett S, Voelker RB, Berglund JA, Staley JP, Baumann P. Intronic sequence elements impede exon ligation and trigger a discard pathway that yields functional telomerase RNA in fission yeast. Genes Dev 2013; 27:627-38. [PMID: 23468430 DOI: 10.1101/gad.212738.112] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
The fission yeast telomerase RNA (TER1) precursor harbors an intron immediately downstream from its mature 3' end. Unlike most introns, which are removed from precursor RNAs by the spliceosome in two sequential but tightly coupled transesterification reactions, TER1 only undergoes the first cleavage reaction during telomerase RNA maturation. The mechanism underlying spliceosome-mediated 3' end processing has remained unclear. We now demonstrate that a strong branch site (BS), a long distance to the 3' splice site (3' SS), and a weak polypyrimidine (Py) tract act synergistically to attenuate the transition from the first to the second step of splicing. The observation that a strong BS antagonizes the second step of splicing in the context of TER1 suggests that the BS-U2 snRNA interaction is disrupted after the first step and thus much earlier than previously thought. The slow transition from first to second step triggers the Prp22 DExD/H-box helicase-dependent rejection of the cleaved products and Prp43-dependent "discard" of the splicing intermediates. Our findings explain how the spliceosome can function in 3' end processing and provide new insights into the mechanism of splicing.
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Affiliation(s)
- Ram Kannan
- Howard Hughes Medical Institute, Stowers Institute for Medical Research, Kansas City, Missouri 64110, USA
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31
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Yang F, Wang XY, Zhang ZM, Pu J, Fan YJ, Zhou J, Query CC, Xu YZ. Splicing proofreading at 5' splice sites by ATPase Prp28p. Nucleic Acids Res 2013; 41:4660-70. [PMID: 23462954 PMCID: PMC3632134 DOI: 10.1093/nar/gkt149] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Fidelity and efficiency of pre-mRNA splicing are critical for generating functional mRNAs, but how such accuracy in 5′ splice site (SS) selection is attained is not fully clear. Through a series of yeast genetic screens, we isolated alleles of prp28 that improve splicing of suboptimal 5′SS substrates, demonstrating that WT-Prp28p proofreads, and consequently rejects, poor 5′SS. Prp28p is thought to facilitate the disruption of 5′SS–U1 snRNA pairing to allow for 5′SS–U6 snRNA pairing in the catalytic spliceosome; unexpectedly, 5′SS proofreading by Prp28p is dependent on competition with the stability of the 5′SS:U6 duplex, but not the 5′SS:U1 duplex. E404K, the strongest prp28 allele containing a mutation located in the linker region between adenosine triphosphatase (ATPase) subdomains, exhibited lower RNA-binding activity and enhanced splicing of suboptimal substrates before first-step catalysis, suggesting that decreased Prp28p activity allows longer time for suboptimal 5′SS substrates to pair with U6 snRNA and thereby reduces splicing fidelity. Residue E404 is critical for providing high splicing activity, demonstrated here in both yeast and Drosophila cells. Thus, the subdomain linker in Prp28p plays important roles both in splicing efficiency across species and in proofreading of 5′SS.
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Affiliation(s)
- Fei Yang
- Key Laboratory of Insect Developmental and Evolutionary Biology, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China
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32
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Nielsen KH, Staley JP. Spliceosome activation: U4 is the path, stem I is the goal, and Prp8 is the keeper. Let's cheer for the ATPase Brr2! Genes Dev 2013; 26:2461-7. [PMID: 23154979 DOI: 10.1101/gad.207514.112] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
During pre-mRNA splicing, the spliceosome is activated for catalysis by unwinding base-paired U4/U6 small nuclear RNAs, a step that must be precisely timed. We know that unwinding requires the ATPase Brr2, but the mechanism and regulation of unwinding have been understood poorly. In the November 1, 2012, issue of Genes & Development, Hahn and colleagues (pp. 2408-2421) and Mozaffari-Jovin and colleagues (pp. 2422-2434) defined a pathway for U4/U6 unwinding. Moreover, Mozaffari-Jovin and colleagues suggested a mechanism for regulating Brr2.
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Affiliation(s)
- Klaus H Nielsen
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, Illinois 60637, USA
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33
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Visualizing group II intron catalysis through the stages of splicing. Cell 2013; 151:497-507. [PMID: 23101623 DOI: 10.1016/j.cell.2012.09.033] [Citation(s) in RCA: 133] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2012] [Revised: 07/13/2012] [Accepted: 09/06/2012] [Indexed: 11/21/2022]
Abstract
Group II introns are self-splicing ribozymes that share a reaction mechanism and a common ancestor with the eukaryotic spliceosome, thereby providing a model system for understanding the chemistry of pre-mRNA splicing. Here we report 14 crystal structures of a group II intron at different stages of catalysis. We provide a detailed mechanism for the first step of splicing, we describe a reversible conformational change between the first and the second steps of splicing, and we present the ligand-free intron structure after splicing in an active state that corresponds to the retrotransposable form of the intron. During each reaction, the reactants are aligned and activated by a heteronuclear four-metal-ion center that contains a metal cluster and obligate monovalent cations, and they adopt a structural arrangement similar to that of protein endonucleases. Based on our data, we propose a model for the splicing cycle and show that it is applicable to the eukaryotic spliceosome.
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34
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Brr2p-mediated conformational rearrangements in the spliceosome during activation and substrate repositioning. Genes Dev 2013; 26:2408-21. [PMID: 23124065 DOI: 10.1101/gad.199307.112] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Brr2p is one of eight RNA helicases involved in pre-mRNA splicing. Detailed understanding of the functions of Brr2p and other spliceosomal helicases has been limited by lack of knowledge of their in vivo substrates. To address this, sites of direct Brr2p-RNA interaction were identified by in vivo UV cross-linking in budding yeast. Cross-links identified in the U4 and U6 small nuclear RNAs (snRNAs) suggest U4/U6 stem I as a Brr2p substrate during spliceosome activation. Further Brr2p cross-links were identified in loop 1 of the U5 snRNA and near splice sites and 3' ends of introns, suggesting the possibility of a previously uncharacterized function for Brr2p in the catalytic center of the spliceosome. Consistent with this, mutant brr2-G858R reduced second-step splicing efficiency and enhanced cross-linking to 3' ends of introns. Furthermore, RNA sequencing indicated preferential inhibition of splicing of introns with structured 3' ends. The Brr2-G858Rp cross-linking pattern in U6 was consistent with an open conformation for the catalytic center of the spliceosome during first-to-second-step transition. We propose a previously unsuspected function for Brr2p in driving conformational rearrangements that lead to competence for the second step of splicing.
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35
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Pérez-Valle J, Vilardell J. Intronic features that determine the selection of the 3' splice site. WILEY INTERDISCIPLINARY REVIEWS-RNA 2012; 3:707-17. [PMID: 22807288 DOI: 10.1002/wrna.1131] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Most eukaryotic primary transcripts include segments, or introns, that will be accurately removed during RNA biogenesis. This process, known as pre-messenger RNA splicing, is catalyzed by the spliceosome, accurately selecting a set of intronic marks from others apparently equivalent. This identification is critical, as incorrectly spliced RNAs can be toxic for the organism. One of these marks, the dinucleotide AG, signals the intronic 3' end, or 3' splice site (ss). In this review we will focus on those intronic features that have an impact on 3' ss selection. These include the location and type of neighboring sequences, and their distance to the 3' end. We will see that their interplay is needed to select the right intronic end, and that this can be modulated by additional intronic elements that contribute to alternative splicing, whereby diverse RNAs can be generated from identical precursors. This complexity, still poorly understood, is fundamental for the accuracy of gene expression. In addition, a clear knowledge of 3' ss selection is needed to fully decipher the coding potential of genomes.
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Affiliation(s)
- Jorge Pérez-Valle
- Department of Molecular Genòmics, Institute of Molecular Biology of Barcelona (IBMB), Barcelona, Spain
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36
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Semlow DR, Staley JP. Staying on message: ensuring fidelity in pre-mRNA splicing. Trends Biochem Sci 2012; 37:263-73. [PMID: 22564363 DOI: 10.1016/j.tibs.2012.04.001] [Citation(s) in RCA: 89] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2011] [Revised: 02/23/2012] [Accepted: 04/03/2012] [Indexed: 12/28/2022]
Abstract
The faithful expression of genes requires that cellular machinery select substrates with high specificity at each step in gene expression. High specificity is particularly important at the stage of nuclear pre-mRNA splicing, during which the spliceosome selects splice sites and excises intervening introns. With low specificity, the usage of alternative sites would yield insertions, deletions and frame shifts in mRNA. Recently, biochemical, genetic and genome-wide approaches have significantly advanced our understanding of splicing fidelity. In particular, we have learned that DExD/H-box ATPases play a general role in rejecting and discarding suboptimal substrates and that these factors serve as a paradigm for proofreading NTPases in other systems. Recent advances have also defined fundamental questions for future investigations.
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Affiliation(s)
- Daniel R Semlow
- Graduate Program in Cell and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA
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37
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Query CC, Konarska MM. CEF1/CDC5 alleles modulate transitions between catalytic conformations of the spliceosome. RNA (NEW YORK, N.Y.) 2012; 18:1001-13. [PMID: 22408182 PMCID: PMC3334688 DOI: 10.1261/rna.029421.111] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Conformational change within the spliceosome is required between the first and second catalytic steps of pre-mRNA splicing. A prior genetic screen for suppressors of an intron mutant that stalls between the two steps yielded both prp8 and non-prp8 alleles that suppressed second-step splicing defects. We have now identified the strongest non-prp8 suppressors as alleles of the NTC (Prp19 complex) component, CEF1. These cef1 alleles generally suppress second-step defects caused by a variety of intron mutations, mutations in U6 snRNA, or deletion of the second-step protein factor Prp17, and they can activate alternative 3' splice sites. Genetic and functional interactions between cef1 and prp8 alleles suggest that they modulate the same event(s) in the first-to-second-step transition, most likely by stabilization of the second-step spliceosome; in contrast, alleles of U6 snRNA that also alter this transition modulate a distinct event, most likely by stabilization of the first-step spliceosome. These results implicate a myb-like domain of Cef1/CDC5 in interactions that modulate conformational states of the spliceosome and suggest that alteration of these events affects splice site use, resulting in alternative splicing-like patterns in yeast.
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Affiliation(s)
- Charles C. Query
- Department of Cell Biology, Albert Einstein College of Medicine, Bronx, New York 10461, USA
- Corresponding authors.E-mail .E-mail .
| | - Maria M. Konarska
- The Rockefeller University, New York, New York 10065, USA
- Corresponding authors.E-mail .E-mail .
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38
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Hoskins AA, Moore MJ. The spliceosome: a flexible, reversible macromolecular machine. Trends Biochem Sci 2012; 37:179-88. [PMID: 22480731 DOI: 10.1016/j.tibs.2012.02.009] [Citation(s) in RCA: 172] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2012] [Revised: 02/27/2012] [Accepted: 02/28/2012] [Indexed: 01/22/2023]
Abstract
With more than a hundred individual RNA and protein parts and a highly dynamic assembly and disassembly pathway, the spliceosome is arguably the most complicated macromolecular machine in the eukaryotic cell. This complexity has made kinetic and mechanistic analysis of splicing incredibly challenging. Yet, recent technological advances are now providing tools for understanding this process in much greater detail. Ranging from genome-wide analyses of splicing and creation of an orthogonal spliceosome in vivo, to purification of active spliceosomes and observation of single molecules in vitro, such new experimental approaches are yielding significant insight into the inner workings of this remarkable machine. These experiments are rewriting the textbooks, with a new picture emerging of a dynamic, malleable machine heavily influenced by the identity of its pre-mRNA substrate.
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Affiliation(s)
- Aaron A Hoskins
- Department of Biochemistry, University of Wisconsin-Madison, WI 53706, USA.
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39
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Burke JE, Sashital DG, Zuo X, Wang YX, Butcher SE. Structure of the yeast U2/U6 snRNA complex. RNA (NEW YORK, N.Y.) 2012; 18:673-83. [PMID: 22328579 PMCID: PMC3312555 DOI: 10.1261/rna.031138.111] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
The U2/U6 snRNA complex is a conserved and essential component of the active spliceosome that interacts with the pre-mRNA substrate and essential protein splicing factors to promote splicing catalysis. Here we have elucidated the solution structure of a 111-nucleotide U2/U6 complex using an approach that integrates SAXS, NMR, and molecular modeling. The U2/U6 structure contains a three-helix junction that forms an extended "Y" shape. The U6 internal stem-loop (ISL) forms a continuous stack with U2/U6 Helices Ib, Ia, and III. The coaxial stacking of Helix Ib on the U6 ISL is a configuration that is similar to the Domain V structure in group II introns. Interestingly, essential features of the complex--including the U80 metal binding site, AGC triad, and pre-mRNA recognition sites--localize to one face of the molecule. This observation suggests that the U2/U6 structure is well-suited for orienting substrate and cofactors during splicing catalysis.
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Affiliation(s)
- Jordan E. Burke
- Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA
| | - Dipali G. Sashital
- Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA
| | - Xiaobing Zuo
- Advanced Photon Source, Argonne National Laboratory, Chicago, Illinois 60437, USA
| | - Yun-Xing Wang
- National Cancer Institute, National Institutes of Health, Frederick, Maryland 21702, USA
| | - Samuel E. Butcher
- Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA
- Corresponding author.E-mail .
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40
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Rasche N, Dybkov O, Schmitzová J, Akyildiz B, Fabrizio P, Lührmann R. Cwc2 and its human homologue RBM22 promote an active conformation of the spliceosome catalytic centre. EMBO J 2012; 31:1591-604. [PMID: 22246180 DOI: 10.1038/emboj.2011.502] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2011] [Accepted: 12/15/2011] [Indexed: 11/09/2022] Open
Abstract
RNA-structural elements play key roles in pre-mRNA splicing catalysis; yet, the formation of catalytically competent RNA structures requires the assistance of spliceosomal proteins. We show that the S. cerevisiae Cwc2 protein functions prior to step 1 of splicing, and it is not required for the Prp2-mediated spliceosome remodelling that generates the catalytically active B complex, suggesting that Cwc2 plays a more sophisticated role in the generation of a functional catalytic centre. In active spliceosomes, Cwc2 contacts catalytically important RNA elements, including the U6 internal stem-loop (ISL), and regions of U6 and the pre-mRNA intron near the 5' splice site, placing Cwc2 at/near the spliceosome's catalytic centre. These interactions are evolutionarily conserved, as shown by studies with Cwc2's human counterpart RBM22, indicating that Cwc2/RBM22-RNA contacts are functionally important. We propose that Cwc2 induces an active conformation of the spliceosome's catalytic RNA elements. Thus, the function of RNA-RNA tertiary interactions within group II introns, namely to induce an active conformation of domain V, may be fulfilled by proteins that contact the functionally analogous U6-ISL, within the spliceosome.
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Affiliation(s)
- Nicolas Rasche
- Department of Cellular Biochemistry, Max-Planck-Institute of Biophysical Chemistry, Göttingen, Germany
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41
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Boehr DD. Promiscuity in protein-RNA interactions: conformational ensembles facilitate molecular recognition in the spliceosome: conformational diversity in U2AF⁶⁵ facilitates binding to diverse RNA sequences. Bioessays 2011; 34:174-80. [PMID: 22144099 DOI: 10.1002/bies.201100152] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Here I discuss findings that suggest a universal mechanism for proteins (and RNA) to recognize and interact with various binding partners by selectively binding to different conformations that pre-exist in the free protein's conformational ensemble. The tandem RNA recognition motif domains of splicing factor U2AF⁶⁵ fluctuate in solution between a predominately closed conformation in which the RNA binding site of one of the domains is blocked, and a lowly populated open conformation in which both RNA binding pockets are accessible. RNA binding to U2AF⁶⁵ may thus occur through the weakly populated open conformation, and the binding interaction stabilizes the open conformation. The conformational diversity observed in U2AF⁶⁵ might also facilitate binding to diverse RNA sequences as found in the polypyrimidine tracts that help define 3' splice sites. Similar binding pathways in other systems have important consequences in biological regulation, molecular evolution, and information storage.
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Affiliation(s)
- David D Boehr
- Department of Chemistry, The Pennsylvania State University, 240 Chemistry Building, University Park, PA, USA.
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Meyer M, Plass M, Pérez-Valle J, Eyras E, Vilardell J. Deciphering 3'ss selection in the yeast genome reveals an RNA thermosensor that mediates alternative splicing. Mol Cell 2011; 43:1033-9. [PMID: 21925391 DOI: 10.1016/j.molcel.2011.07.030] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2011] [Revised: 06/06/2011] [Accepted: 07/27/2011] [Indexed: 12/17/2022]
Abstract
Poor understanding of the spliceosomal mechanisms to select intronic 3' ends (3'ss) is a major obstacle to deciphering eukaryotic genomes. Here, we discern the rules for global 3'ss selection in yeast. We show that, in contrast to the uniformity of yeast splicing, the spliceosome uses all available 3'ss within a distance window from the intronic branch site (BS), and that in ∼70% of all possible 3'ss this is likely to be mediated by pre-mRNA structures. Our results reveal that one of these RNA folds acts as an RNA thermosensor, modulating alternative splicing in response to heat shock by controlling alternate 3'ss availability. Thus, our data point to a deeper role for the pre-mRNA in the control of its own fate, and to a simple mechanism for some alternative splicing.
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Affiliation(s)
- Markus Meyer
- Centre de Regulació Genòmica, Dr. Aiguader 88, 08003 Barcelona, Spain
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Hoskins AA, Gelles J, Moore MJ. New insights into the spliceosome by single molecule fluorescence microscopy. Curr Opin Chem Biol 2011; 15:864-70. [PMID: 22057211 DOI: 10.1016/j.cbpa.2011.10.010] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2011] [Revised: 10/10/2011] [Accepted: 10/17/2011] [Indexed: 11/17/2022]
Abstract
Splicing is an essential eukaryotic process in which introns are excised from precursors to messenger RNAs and exons ligated together. This reaction is catalyzed by a multi-MegaDalton machine called the spliceosome, composed of 5 small nuclear RNAs (snRNAs) and a core set of ∼100 proteins minimally required for activity. Because of the spliceosome's size, its low abundance in cellular extracts, and its highly dynamic assembly pathway, analysis of the kinetics of splicing and the conformational rearrangements occurring during spliceosome assembly and disassembly has proven extraordinarily challenging. Here, we review recent progress in combining chemical biology methodologies with single molecule fluorescence techniques to provide a window into splicing in real time. These methods complement ensemble measurements of splicing in vivo and in vitro to facilitate kinetic dissection of pre-mRNA splicing.
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MESH Headings
- Biotin/chemistry
- Biotin/metabolism
- Exons
- Fluorescence Resonance Energy Transfer
- Fluorescent Dyes/analysis
- Fluorescent Dyes/chemistry
- Introns
- Microscopy, Fluorescence/methods
- RNA Precursors/analysis
- RNA Precursors/chemistry
- RNA Precursors/metabolism
- RNA Splicing/genetics
- RNA, Fungal/analysis
- RNA, Fungal/chemistry
- RNA, Fungal/metabolism
- RNA, Small Nuclear/analysis
- RNA, Small Nuclear/chemistry
- RNA, Small Nuclear/metabolism
- Ribonucleoproteins, Small Nuclear/analysis
- Ribonucleoproteins, Small Nuclear/chemistry
- Ribonucleoproteins, Small Nuclear/metabolism
- Saccharomyces cerevisiae/genetics
- Saccharomyces cerevisiae/metabolism
- Spliceosomes/chemistry
- Spliceosomes/genetics
- Spliceosomes/metabolism
- Staining and Labeling/methods
- Streptavidin/chemistry
- Streptavidin/metabolism
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Affiliation(s)
- Aaron A Hoskins
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, 364 Plantation St., Worcester, MA 01605, USA.
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Horowitz DS. The mechanism of the second step of pre-mRNA splicing. WILEY INTERDISCIPLINARY REVIEWS-RNA 2011; 3:331-50. [PMID: 22012849 DOI: 10.1002/wrna.112] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The molecular mechanisms of the second step of pre-mRNA splicing in yeast and higher eukaryotes are reviewed. The important elements in the pre-mRNA, the participating proteins, and the proposed secondary structures and roles of the snRNAs are described. The sequence of events in the second step is presented, focusing on the actions of the proteins in setting up and facilitating the second reaction. Mechanisms for avoiding errors in splicing are discussed.
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Affiliation(s)
- David S Horowitz
- Department of Biochemistry and Molecular Biology, Uniformed Services University of the Health Sciences, Bethesda, MD 20814, USA.
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Abstract
Pre-mRNA splicing is catalyzed by the spliceosome, a multimegadalton ribonucleoprotein (RNP) complex comprised of five snRNPs and numerous proteins. Intricate RNA-RNA and RNP networks, which serve to align the reactive groups of the pre-mRNA for catalysis, are formed and repeatedly rearranged during spliceosome assembly and catalysis. Both the conformation and composition of the spliceosome are highly dynamic, affording the splicing machinery its accuracy and flexibility, and these remarkable dynamics are largely conserved between yeast and metazoans. Because of its dynamic and complex nature, obtaining structural information about the spliceosome represents a major challenge. Electron microscopy has revealed the general morphology of several spliceosomal complexes and their snRNP subunits, and also the spatial arrangement of some of their components. X-ray and NMR studies have provided high resolution structure information about spliceosomal proteins alone or complexed with one or more binding partners. The extensive interplay of RNA and proteins in aligning the pre-mRNA's reactive groups, and the presence of both RNA and protein at the core of the splicing machinery, suggest that the spliceosome is an RNP enzyme. However, elucidation of the precise nature of the spliceosome's active site, awaits the generation of a high-resolution structure of its RNP core.
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Affiliation(s)
- Cindy L Will
- Max Planck Institute for Biophysical Chemistry, Department of Cellular Biochemistry, Am Fassberg 11, 37077 Göttingen, Germany
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Corrionero A, Miñana B, Valcárcel J. Reduced fidelity of branch point recognition and alternative splicing induced by the anti-tumor drug spliceostatin A. Genes Dev 2011; 25:445-59. [PMID: 21363963 DOI: 10.1101/gad.2014311] [Citation(s) in RCA: 205] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Spliceostatin A (SSA) is a stabilized derivative of a Pseudomonas bacterial fermentation product that displays potent anti-proliferative and anti-tumor activities in cancer cells and animal models. The drug inhibits pre-mRNA splicing in vitro and in vivo and binds SF3b, a protein subcomplex of U2 small nuclear ribonucleoprotein (snRNP), which is essential for recognition of the pre-mRNA branch point. We report that SSA prevents interaction of an SF3b 155-kDa subunit with the pre-mRNA, concomitant with nonproductive recruitment of U2 snRNP to sequences 5' of the branch point. Differences in base-pairing potential with U2 snRNA in this region lead to different sensitivity of 3' splice sites to SSA, and to SSA-induced changes in alternative splicing. Indeed, rather than general splicing inhibition, splicing-sensitive microarray analyses reveal specific alternative splicing changes induced by the drug that significantly overlap with those induced by knockdown of SF3b 155. These changes lead to down-regulation of genes important for cell division, including cyclin A2 and Aurora A kinase, thus providing an explanation for the anti-proliferative effects of SSA. Our results reveal a mechanism that prevents nonproductive base-pairing interactions in the spliceosome, and highlight the regulatory and cancer therapeutic potential of perturbing the fidelity of splice site recognition.
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Genomic mRNA profiling reveals compensatory mechanisms for the requirement of the essential splicing factor U2AF. Mol Cell Biol 2010; 31:652-61. [PMID: 21149581 DOI: 10.1128/mcb.01000-10] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The large subunit of the U2 auxiliary factor (U2AF) recognizes the polypyrimidine tract (Py-tract) located adjacent to the 3' splice site to facilitate U2 snRNP recruitment. While U2AF is considered essential for pre-mRNA splicing, its requirement for splicing on a genome-wide level has not been analyzed. Using Solexa sequencing, we performed mRNA profiling for splicing in the Schizosaccharomyces pombe U2AF(59) (prp2.1) temperature-sensitive mutant. Surprisingly, our analysis revealed that introns show a range of splicing defects in the mutant strain. While U2AF(59) inactivation (nonpermissive) conditions inhibit splicing of some introns, others are spliced apparently normally. Bioinformatics analysis indicated that U2AF(59)-insensitive introns have stronger 5' splice sites and higher A/U content. Most importantly, features that contribute to U2AF(59) insensitivity of an intron unexpectedly reside in its 5'-most 30 nucleotides. These include the 5' splice site, a guanosine at position 7, and the 5' splice site-to-branch point sequence context. A differential requirement (similar to U2AF(59)) for introns may also apply to other general splicing factors (e.g., prp10). Our combined results indicate that U2AF insensitivity is a common phenomenon and that varied intron features support the existence of unrecognized aspects of spliceosome assembly.
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Valadkhan S, Jaladat Y. The spliceosomal proteome: at the heart of the largest cellular ribonucleoprotein machine. Proteomics 2010; 10:4128-41. [PMID: 21080498 DOI: 10.1002/pmic.201000354] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Almost all primary transcripts in higher eukaryotes undergo several splicing events and alternative splicing is a major factor in generating proteomic diversity. Thus, the spliceosome, the ribonucleoprotein assembly that performs splicing, is a highly critical cellular machine and as expected, a very complex one. Indeed, the spliceosome is one of the largest, if not the largest, molecular machine in the cell with over 150 different components in human. A large fraction of the spliceosomal proteome is organized into small nuclear ribonucleoprotein particles by associating with one of the small nuclear RNAs, and the function of many spliceosomal proteins revolve around their association or interaction with the spliceosomal RNAs or the substrate pre-messenger RNAs. In addition to the complex web of protein-RNA interactions, an equally complex network of protein-protein interactions exists in the spliceosome, which includes a number of large, conserved proteins with critical functions in the spliceosomal catalytic core. These include the largest conserved nuclear protein, Prp8, which plays a critical role in spliceosomal function in a hitherto unknown manner. Taken together, the large spliceosomal proteome and its dynamic nature has made it a highly challenging system to study, and at the same time, provides an exciting example of the evolution of a proteome around a backbone of primordial RNAs likely dating from the RNA World.
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Affiliation(s)
- Saba Valadkhan
- Center for RNA Molecular Biology, Case Western Reserve University, Cleveland, OH 44113, USA.
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Lee C, Jaladat Y, Mohammadi A, Sharifi A, Geisler S, Valadkhan S. Metal binding and substrate positioning by evolutionarily invariant U6 sequences in catalytically active protein-free snRNAs. RNA (NEW YORK, N.Y.) 2010; 16:2226-38. [PMID: 20826700 PMCID: PMC2957061 DOI: 10.1261/rna.2170910] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2010] [Accepted: 07/31/2010] [Indexed: 05/20/2023]
Abstract
We have previously shown that a base-paired complex formed by two of the spliceosomal RNA components, U6 and U2 small nuclear RNAs (snRNAs), can catalyze a two-step splicing reaction that depended on an evolutionarily invariant region in U6, the ACAGAGA box. Here we further analyze this RNA-catalyzed reaction and show that while the 5' and 3' splice site substrates are juxtaposed and positioned near the ACAGAGA sequence in U6, the role of the snRNAs in the reaction is beyond mere juxtaposition of the substrates and likely involves the formation of a sophisticated active site. Interestingly, the snRNA-catalyzed reaction is metal dependent, as is the case with other known splicing RNA enzymes, and terbium(III) cleavage reactions indicate metal binding by the U6/U2 complex within the evolutionarily conserved regions of U6. The above results, combined with the structural similarities between U6 and catalytically critical domains in group II self-splicing introns, suggest that the base-paired complex of U6 and U2 snRNAs is a vestigial ribozyme and a likely descendant of a group II-like self-splicing intron.
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Affiliation(s)
- Caroline Lee
- Center for RNA Molecular Biology, Case Western Reserve University, Cleveland, Ohio 44106, USA
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50
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Abstract
RNAs and RNA-protein complexes (RNPs) traverse rugged energy landscapes as they fold to their native structures, and many continue to undergo conformational rearrangements as they function. Due to the inherent stability of local RNA structure, proteins are required to assist with RNA conformational transitions during initial folding and in exchange between functional structures. DEAD-box proteins are superfamily 2 RNA helicases that are ubiquitously involved in RNA-mediated processes. Some of these proteins use an ATP-dependent cycle of conformational changes to disrupt RNA structure nonprocessively, accelerating structural transitions of RNAs and RNPs in a manner that bears a strong resemblance to the activities of certain groups of protein chaperones. This review summarizes recent work using model substrates and tractable self-splicing intron RNAs, which has given new insights into how DEAD-box proteins promote RNA folding steps and conformational transitions, and it summarizes recent progress in identifying sites and mechanisms of DEAD-box protein activity within more complex cellular targets.
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Affiliation(s)
- Cynthia Pan
- Department of Chemistry and Biochemistry, University of Texas, Austin, TX, USA
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