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Hu Z, Leppla SH, Li B, Elkins CA. Antibodies specific for nucleic acids and applications in genomic detection and clinical diagnostics. Expert Rev Mol Diagn 2014; 14:895-916. [PMID: 25014728 DOI: 10.1586/14737159.2014.931810] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Detection of nucleic acids using antibodies is uncommon. This is in part because nucleic acids are poor immunogens and it is difficult to elicit antibodies having high affinity to each type of nucleic acid while lacking cross-reactivity to others. We describe the origins and applications of a variety of anti-nucleic acid antibodies, including ones reacting with modified nucleosides and nucleotides, single-stranded DNA, double-stranded DNA, RNA, DNA:RNA hybrids, locked-nucleic acids or peptide nucleic acid:nucleic acid hybrids. Carefully selected antibodies can be excellent reagents for detecting bacteria, viruses, small RNAs, microRNAs, R-loops, cancer cells, stem cells, apoptotic cells and so on. The detection may be sensitive, simple, rapid, specific, reproducible, quantitative and cost-effective. Current microarray and diagnostic methods that depend on cDNA or cRNA can be replaced by using antibody detection of nucleic acids. Therefore, development should be encouraged to explore new utilities and create a robust arsenal of new anti-nucleic acid antibodies.
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Affiliation(s)
- Zonglin Hu
- Winchester Engineering & Analytical Center, Office of Regulatory Affairs, US Food and Drug Administration, 109 Holton Street, Winchester, MA 01890, USA
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2
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Mesa A, Somarelli JA, Wu W, Martinez L, Blom MB, Greidinger EL, Herrera RJ. Differential immunoglobulin class-mediated responses to components of the U1 small nuclear ribonucleoprotein particle in systemic lupus erythematosus and mixed connective tissue disease. Lupus 2014; 22:1371-81. [PMID: 24158973 DOI: 10.1177/0961203313508444] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
OBJECTIVE The objective of this paper is to determine whether patients with systemic lupus erythematosus (SLE) and mixed connective tissue disease (MCTD) possess differential IgM- and IgG-specific reactivity against peptides from the U1 small nuclear ribonucleoprotein particle (U1 snRNP). METHODS The IgM- and IgG-mediated responses against 15 peptides from subunits of the U1 snRNP were assessed by indirect enzyme linked immunosorbent assays (ELISAs) in sera from patients with SLE and MCTD and healthy individuals (n = 81, 41, and 31, respectively). Additionally, 42 laboratory tests and 40 clinical symptoms were evaluated to uncover potential differences. Binomial logistic regression analyses (BLR) were performed to construct models to support the independent nature of SLE and MCTD. Receiver operating characteristic (ROC) curves corroborated the classification power of the models. RESULTS We analyzed IgM and IgG anti-U1 snRNP titers to classify SLE and MCTD patients. IgG anti-U1 snRNP reactivity segregates SLE and MCTD from nondisease controls with an accuracy of 94.1% while IgM-specific anti-U1 snRNP responses distinguish SLE from MCTD patients with an accuracy of 71.3%. Comparison of the IgG and IgM anti-U1 snRNP approach with clinical tests used for diagnosing SLE and MCTD revealed that our method is the best classification tool of those analyzed (p ≤ 0.0001). CONCLUSIONS Our IgM anti-U1 snRNP system along with lab tests and symptoms provide additional molecular and clinical evidence to support the hypothesis that SLE and MCTD may be distinct syndromes.
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Affiliation(s)
- A Mesa
- 1Department of Biological Sciences, Florida International University, USA
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3
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Kattah NH, Kattah MG, Utz PJ. The U1-snRNP complex: structural properties relating to autoimmune pathogenesis in rheumatic diseases. Immunol Rev 2010; 233:126-45. [PMID: 20192997 PMCID: PMC3074261 DOI: 10.1111/j.0105-2896.2009.00863.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The U1 small nuclear ribonucleoprotein particle (snRNP) is a target of autoreactive B cells and T cells in several rheumatic diseases including systemic lupus erythematosus (SLE) and mixed connective tissue disease (MCTD). We propose that inherent structural properties of this autoantigen complex, including common RNA-binding motifs, B and T-cell epitopes, and a unique stimulatory RNA molecule, underlie its susceptibility as a target of the autoimmune response. Immune mechanisms that may contribute to overall U1-snRNP immunogenicity include epitope spreading through B and T-cell interactions, apoptosis-induced modifications, and toll-like receptor (TLR) activation through stimulation by U1-snRNA. We conclude that understanding the interactions between U1-snRNP and the immune system will provide insights into why certain patients develop anti-U1-snRNP autoimmunity, and more importantly how to effectively target therapies against this autoimmune response.
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Affiliation(s)
- Nicole H Kattah
- Division of Immunology and Rheumatology, Department of Medicine, Stanford University, Stanford, CA 94305, USA.
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4
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Vollmer J, Tluk S, Schmitz C, Hamm S, Jurk M, Forsbach A, Akira S, Kelly KM, Reeves WH, Bauer S, Krieg AM. Immune stimulation mediated by autoantigen binding sites within small nuclear RNAs involves Toll-like receptors 7 and 8. ACTA ACUST UNITED AC 2006; 202:1575-85. [PMID: 16330816 PMCID: PMC2213330 DOI: 10.1084/jem.20051696] [Citation(s) in RCA: 424] [Impact Index Per Article: 23.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the production of autoantibodies to certain cellular macromolecules, such as the small nuclear ribonucleoprotein particles (snRNPs), which had been considered to be passive targets of the autoimmune response. SLE is also characterized by the increased expression of type I interferon (IFN), which appears to be associated with the development and severity of disease. Here, we show that specific, highly conserved RNA sequences within snRNPs can stimulate Toll-like receptors (TLRs) 7 and 8 as well as activate innate immune cells, such as plasmacytoid dendritic cells (pDCs), which respond by secreting high levels of type I IFN. SLE patient sera containing autoantibodies to snRNPs form immune complexes that are taken up through the Fc receptor γRII and efficiently stimulate pDCs to secrete type I IFNs. These results demonstrate that a prototype autoantigen, the snRNP, can directly stimulate innate immunity and suggest that autoantibodies against snRNP may initiate SLE by stimulating TLR7/8.
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Affiliation(s)
- Jörg Vollmer
- Coley Pharmaceutical GmbH, 40764 Langenfeld, Germany
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5
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Stark H, Dube P, Lührmann R, Kastner B. Arrangement of RNA and proteins in the spliceosomal U1 small nuclear ribonucleoprotein particle. Nature 2001; 409:539-42. [PMID: 11206553 DOI: 10.1038/35054102] [Citation(s) in RCA: 191] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2000] [Accepted: 11/17/2000] [Indexed: 11/08/2022]
Abstract
In eukaryotic cells, freshly synthesized messenger RNA (pre-mRNA) contains stretches of non-coding RNA that must be excised before the RNA can be translated into protein. Their removal is catalysed by the spliceosome, a large complex formed when a number of small nuclear ribonucleoprotein particles (snRNPs) bind sequentially to the pre-mRNA. The first snRNP to bind is called U1; other snRNPs (U2, U4/U6 and U5) follow. Here we describe the three-dimensional structure of human U1 snRNP, determined by single-particle electron cryomicroscopy at 10 A resolution. The reconstruction reveals a doughnut-shaped central element that accommodates the seven Sm proteins common to all snRNPs, supporting a proposed model of circular Sm protein arrangement. By taking earlier biochemical results into account, we were able to assign the remaining density of the map to the other known components of U1 snRNP, deriving a structural model that describes the three-dimensional arrangement of proteins and RNA in U1 snRNP.
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Affiliation(s)
- H Stark
- Institut für Molekularbiologie und Tumorforschung, Marburg, Germany.
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6
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Abstract
Myositis-specific autoantibodies or myositis-associated autoantibodies can often be found in serum of patients with polymyositis and dermatomyositis. The presence of these autoantibodies can be significant in patient diagnosis and classification. Recent studies have provided new information about many of these specific autoantibodies. Among the more important developments were identification of a new antisynthetase, reacting with asparaginyl-tRNA synthetase; the detection of antibodies to the tRNA(his) in a over a third of anti-Jo-1 sera; and the description of distinctive features of the histopathology of patients with anti-Jo-1. New information about the cellular role of the antigens was discovered, including a role for Mi-2 antigen in chromosomally-mediated regulation of transcription as part of a nucleosome remodeling complex, and a potential role for PM-Scl antigen in ribosomal RNA processing as part of an exosome. The reason for the production of the autoantibodies, and the reason particular antigens are targeted, are key questions. Recent studies have suggested that antigen cleavage during apoptosis, particularly by granzyme B, may be an important factor. Whether the antibodies play a role in tissue injury remains unknown.
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Affiliation(s)
- I N Targoff
- Veterans Affairs Medical Center, Oklahoma City, University of Oklahoma Health Sciences Center, Oklahoma Medical Research Foundation, 73104, USA.
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7
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Abstract
In prokaryotic ribosomal RNAs, most UUCG tetraloops are closed by a C-G base-pair. However, this preference is greatly reduced in eukaryotic rRNA species where many UUCG tetraloops are closed by G-C base-pairs. Here, biophysical properties of the C[UUCG]G and G[UUCG]C tetraloops are compared, using experimental and computational methods. Thermal denaturation experiments are used to derive thermodynamic parameters for the wild-type G[UUCG]C tetraloop and variants containing single deoxy substitutions in the loop. A comparison with analogous experiments on the C[UUCG]G motif shows that the two RNA species exhibit similar patterns in response to the substitutions, suggesting that their loop structures are similar. This conclusion is supported by NMR data that suggest that the essential UUCG loop structure is maintained in both tetraloops. However, NMR results show that the G[UUCG]C loop structure is disrupted prior to melting of the stem; this behavior is in contrast to the two-state behavior of the C[UUCG]G molecule. Stochastic dynamics simulations using the GB/SA continuum solvation model, run as a function of temperature, show rare conformational transitions in several G[UUCG]C simulations. These results lead to the conclusion that substitution of a G-C for a C-G closing base-pair increases the intrinsic flexibility of the UUCG loop.
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Affiliation(s)
- D J Williams
- Department of Biochemistry, Washington University School of Medicine, St Louis, MO 63110, USA
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Degen WG, Aarssen Y, Pruijn GJ, Utz PJ, van Venrooij WJ. The fate of U1 snRNP during anti-Fas induced apoptosis: specific cleavage of the U1 snRNA molecule. Cell Death Differ 2000; 7:70-9. [PMID: 10713722 DOI: 10.1038/sj.cdd.4400617] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
During apoptosis, the U1-70K protein, a component of the spliceosomal U1 snRNP complex, is specifically cleaved by the enzyme caspase-3, converting it into a C-terminally truncated 40-kDa fragment. In this study, we show that the 40-kDa U1-70K fragment is still associated with the complete U1 snRNP complex, and that no obvious modifications occur with the U1 snRNP associated proteins U1A, U1C and Sm-B/B'. Furthermore, it is described for the first time that the U1 snRNA molecule, which is the backbone of the U1 snRNP complex, is modified during apoptosis by the specific removal of the first 5 - 6 nucleotides including the 2,2, 7-trimethylguanosine (TMG) cap. The observations that U1 snRNA cleavage is very specific (no such modifications were detected for the other U snRNAs tested) and that U1 snRNA cleavage is markedly inhibited in the presence of caspase inhibitors, indicate that an apoptotically activated ribonuclease is responsible for the specific modification of U1 snRNA during apoptosis.
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Affiliation(s)
- W G Degen
- Department of Biochemistry, University of Nijmegen, NL-6500 HB Nijmegen, The Netherlands.
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Hoet RMA, Pieffers M, Stassen MHW, Raats J, de Wildt R, Pruijn GJM, van den Hoogen F, van Venrooij WJ. The Importance of the Light Chain for the Epitope Specificity of Human Anti-U1 Small Nuclear RNA Autoantibodies Present in Systemic Lupus Erythematosus Patients. THE JOURNAL OF IMMUNOLOGY 1999. [DOI: 10.4049/jimmunol.163.6.3304] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Abstract
Abs to U1 RNA are frequently found in patients suffering from systemic lupus erythematosus overlap syndromes and Ab titers correlate with disease activity. We describe the isolation of the first human anti-U1 RNA autoantibodies from a combinatorial IgG library made from the bone marrow of a systemic lupus erythematosus patient. With the use of phage display technology, two anti-U1 RNA single-chain variable fragment (scFv) Abs were selected. Both high affinity anti-U1 RNA Ab fragments (Kd ∼ 1 nM) recognize stem II of U1 RNA and were derived from the same heavy chain gene (VH3–11) and the same λ (3r) light chain gene although somatic mutations, predominantly present in the complementarity-determining regions, are different. Experiments, in which the heavy chain genes of both anti-U1 RNA scFvs were reshuffled with the original light chain repertoire of the patient resulted, after selection on stem loop II, in a large number of RNA-binding Ab fragments. All these stem loop II-specific RNA binding clones used a similar, but not identical, 3r λ light chain. When scFvs were selected from the reshuffled libraries by stem loop IV, representing the other autoantigenic site of U1 RNA, most selected Ab clones did react with stem loop IV, but no longer with stem loop II. The stem loop IV-reactive Ab clones contained different, not 3r-related, light chains. These results point to a major role for the light chain in determining the sequence specificity of these disease-related anti-U1 RNA Abs. The possibility that secondary light chain rearrangements are involved in this autoimmune response is discussed.
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Affiliation(s)
- René M. A. Hoet
- *Department of Biochemistry, University of Nijmegen, Nijmegen, The Netherlands; Department of Rheumatology, University Hospital Nijmegen, Nijmegen, The Netherlands; and
- ‡Department of Pathology, University Hospital Maastricht, Maastricht, The Netherlands
| | - Martijn Pieffers
- *Department of Biochemistry, University of Nijmegen, Nijmegen, The Netherlands; Department of Rheumatology, University Hospital Nijmegen, Nijmegen, The Netherlands; and
| | - Maurice H. W. Stassen
- *Department of Biochemistry, University of Nijmegen, Nijmegen, The Netherlands; Department of Rheumatology, University Hospital Nijmegen, Nijmegen, The Netherlands; and
| | - Jos Raats
- *Department of Biochemistry, University of Nijmegen, Nijmegen, The Netherlands; Department of Rheumatology, University Hospital Nijmegen, Nijmegen, The Netherlands; and
| | - Ruud de Wildt
- *Department of Biochemistry, University of Nijmegen, Nijmegen, The Netherlands; Department of Rheumatology, University Hospital Nijmegen, Nijmegen, The Netherlands; and
| | - Ger J. M. Pruijn
- *Department of Biochemistry, University of Nijmegen, Nijmegen, The Netherlands; Department of Rheumatology, University Hospital Nijmegen, Nijmegen, The Netherlands; and
| | - Frank van den Hoogen
- ‡Department of Pathology, University Hospital Maastricht, Maastricht, The Netherlands
| | - Walther J. van Venrooij
- *Department of Biochemistry, University of Nijmegen, Nijmegen, The Netherlands; Department of Rheumatology, University Hospital Nijmegen, Nijmegen, The Netherlands; and
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Teunissen SW, Stassen MH, Pruijn GJ, van Venrooij WJ, Hoet RM. Characterization of an anti-RNA recombinant autoantibody fragment (scFv) isolated from a phage display library and detailed analysis of its binding site on U1 snRNA. RNA (NEW YORK, N.Y.) 1998; 4:1124-1133. [PMID: 9740130 PMCID: PMC1369687 DOI: 10.1017/s1355838298980633] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
This is the first study in which the complex of a monoclonal autoantibody fragment and its target, stem loop II of U1 snRNA, was investigated with enzymatic and chemical probing. A phage display antibody library derived from bone marrow cells of an SLE patient was used for selection of scFvs specific for stem loop II. The scFv specificity was tested by RNA immunoprecipitation and nitrocellulose filter binding competition experiments. Immunofluorescence data and immunoprecipitation of U1 snRNPs containing U1A protein, pointed to an scFv binding site different from the U1A binding site. The scFv binding site on stem loop II was determined by footprinting experiments using RNase A, RNase V1, and hydroxyl radicals. The results show that the binding site covers three sequence elements on the RNA, one on the 5' strand of the stem and two on the 3' strand. Hypersensitivity of three loop nucleotides suggests a conformational change of the RNA upon antibody binding. A three-dimensional representation of stem loop II reveals a juxtapositioning of the three protected regions on one side of the helix, spanning approximately one helical turn. The location of the scFv binding site on stem loop II is in full agreement with the finding that both the U1A protein and the scFv are able to bind stem loop II simultaneously. As a consequence, this recombinant monoclonal anti-U1 snRNA scFv might be very useful in studies on U1 snRNPs and its involvement in cellular processes like splicing.
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Affiliation(s)
- S W Teunissen
- Department of Biochemistry, University of Nijmegen, The Netherlands.
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11
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Herrmann M, Voll RE, Zoller OM, Hagenhofer M, Ponner BB, Kalden JR. Impaired phagocytosis of apoptotic cell material by monocyte-derived macrophages from patients with systemic lupus erythematosus. ARTHRITIS AND RHEUMATISM 1998; 41:1241-50. [PMID: 9663482 DOI: 10.1002/1529-0131(199807)41:7<1241::aid-art15>3.0.co;2-h] [Citation(s) in RCA: 589] [Impact Index Per Article: 22.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
OBJECTIVE To investigate whether the established impaired phagocyte function in systemic lupus erythematosus (SLE) patients also affects apoptotic cell clearance. Accumulation of apoptotic waste as a source for autoantigens that induce and maintain autoimmune responses is discussed. METHODS Apoptosis was detected by morphology and propidium iodide staining. In vitro phagocytosis of autologous apoptotic cells in cultured peripheral blood mononuclear cells was evaluated microscopically. Cross-feeding experiments were performed to investigate phagocytosis of heterologous apoptotic cells by in vitro-differentiated macrophages. Furthermore, the effect of annexin V on the phagocytosis of apoptotic cells was investigated. RESULTS Reduced clearance of apoptotic cells in SLE patients was observed. The defective clearance appeared to reflect phagocyte dysfunction and not an abnormal execution of apoptosis. A similar picture was seen when in vitro-differentiated macrophages from control populations were treated with annexin V. CONCLUSION Noninflammatory engulfment phagocytosis of apoptotic cells is decreased in SLE patients. Persistently circulating apoptotic waste may encounter inflammatory removal pathways and serve as immunogen for the induction of autoreactive lymphocytes and as antigen for immune complex formation.
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Affiliation(s)
- M Herrmann
- Friedrich Alexander University of Erlangen-Nuremberg, Erlangen, Germany
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12
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Plessel G, Lührmann R, Kastner B. Electron microscopy of assembly intermediates of the snRNP core: morphological similarities between the RNA-free (E.F.G) protein heteromer and the intact snRNP core. J Mol Biol 1997; 265:87-94. [PMID: 9020971 DOI: 10.1006/jmbi.1996.0713] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
All four spliceosomal small nuclear ribonucleoproteins (snRNPs) U1, U2, U4/U6 and U5 contain a common structural element called the snRNP core. This core is assembled from the common snRNP proteins and the small nuclear RNA (snRNA). We have used electron microscopy to study the structure of two intermediates of the snRNP core assembly pathway: (1) the (E.F.G) protein complex, which contains only the smallest common proteins E, F and G; and (2) the subscore of U5 snRNP, in which the U5 RNA and the common proteins D1 and D2 are bound to the (E.F.G) protein complex. The general structure of the subscore was found to resemble that of the complete snRNP core, which contains the components of the subscore plus the common proteins B/B' and D3. Both the complete snRNP core and subscore particles are globular, with diameters of 7 to 8 nm. They show a characteristic accumulation of stain at the centre. However, some subscore images showed nicked outlines not seen with the complete snRNP cores. The (E.F.G) protein complex appeared as a ring, with an outer diameter of about 7 nm and a central hole 2 nm across. The molecular dimensions of the E, F and G proteins imply that the thickness of the (E.F.G) ring structure is only about 2 nm. Comparison of the (E.F.G) structure complex with the snRNP core and subcore structures implicates that a flat side of the ring-shaped (E.F.G) complex provides the assembly site(s) for the other components of the snRNP during core assembly: first for the D1 and D2 proteins (and probably the snRNA) during subscore formation, and then for the B/B' and D3 proteins in the completion of the snRNP core particle.
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MESH Headings
- Centrifugation, Density Gradient
- HeLa Cells
- Humans
- Microscopy, Electron
- Protein Conformation
- RNA, Small Nuclear/metabolism
- RNA, Small Nuclear/ultrastructure
- Ribonucleoprotein, U1 Small Nuclear/metabolism
- Ribonucleoprotein, U1 Small Nuclear/ultrastructure
- Ribonucleoprotein, U2 Small Nuclear/genetics
- Ribonucleoprotein, U2 Small Nuclear/metabolism
- Ribonucleoprotein, U5 Small Nuclear/metabolism
- Ribonucleoprotein, U5 Small Nuclear/ultrastructure
- Ribonucleoproteins, Small Nuclear/metabolism
- Ribonucleoproteins, Small Nuclear/ultrastructure
- Spliceosomes
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Affiliation(s)
- G Plessel
- Institut für Molekularbiologie und Tumorforschung, Philipps-Universität Marburg, Germany
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Roy J, Zheng B, Rymond BC, Woolford JL. Structurally related but functionally distinct yeast Sm D core small nuclear ribonucleoprotein particle proteins. Mol Cell Biol 1995; 15:445-55. [PMID: 7799953 PMCID: PMC231989 DOI: 10.1128/mcb.15.1.445] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Spliceosome assembly during pre-mRNA splicing requires the correct positioning of the U1, U2, U4/U6, and U5 small nuclear ribonucleoprotein particles (snRNPs) on the precursor mRNA. The structure and integrity of these snRNPs are maintained in part by the association of the snRNAs with core snRNP (Sm) proteins. The Sm proteins also play a pivotal role in metazoan snRNP biogenesis. We have characterized a Saccharomyces cerevisiae gene, SMD3, that encodes the core snRNP protein Smd3. The Smd3 protein is required for pre-mRNA splicing in vivo. Depletion of this protein from yeast cells affects the levels of U snRNAs and their cap modification, indicating that Smd3 is required for snRNP biogenesis. Smd3 is structurally and functionally distinct from the previously described yeast core polypeptide Smd1. Although Smd3 and Smd1 are both associated with the spliceosomal snRNPs, overexpression of one cannot compensate for the loss of the other. Thus, these two proteins have distinct functions. A pool of Smd3 exists in the yeast cytoplasm. This is consistent with the possibility that snRNP assembly in S. cerevisiae, as in metazoans, is initiated in the cytoplasm from a pool of RNA-free core snRNP protein complexes.
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Affiliation(s)
- J Roy
- Department of Biological Sciences, Carnegie-Mellon University, Pittsburgh, Pennsylvania 15213
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