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Sperber HS, Welke RW, Petazzi RA, Bergmann R, Schade M, Shai Y, Chiantia S, Herrmann A, Schwarzer R. Self-association and subcellular localization of Puumala hantavirus envelope proteins. Sci Rep 2019; 9:707. [PMID: 30679542 PMCID: PMC6345964 DOI: 10.1038/s41598-018-36879-y] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2017] [Accepted: 11/28/2018] [Indexed: 01/08/2023] Open
Abstract
Hantavirus assembly and budding are governed by the surface glycoproteins Gn and Gc. In this study, we investigated the glycoproteins of Puumala, the most abundant Hantavirus species in Europe, using fluorescently labeled wild-type constructs and cytoplasmic tail (CT) mutants. We analyzed their intracellular distribution, co-localization and oligomerization, applying comprehensive live, single-cell fluorescence techniques, including confocal microscopy, imaging flow cytometry, anisotropy imaging and Number&Brightness analysis. We demonstrate that Gc is significantly enriched in the Golgi apparatus in absence of other viral components, while Gn is mainly restricted to the endoplasmic reticulum (ER). Importantly, upon co-expression both glycoproteins were found in the Golgi apparatus. Furthermore, we show that an intact CT of Gc is necessary for efficient Golgi localization, while the CT of Gn influences protein stability. Finally, we found that Gn assembles into higher-order homo-oligomers, mainly dimers and tetramers, in the ER while Gc was present as mixture of monomers and dimers within the Golgi apparatus. Our findings suggest that PUUV Gc is the driving factor of the targeting of Gc and Gn to the Golgi region, while Gn possesses a significantly stronger self-association potential.
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Affiliation(s)
- Hannah Sabeth Sperber
- Institute for Biology, IRI Life Science, Humboldt-Universität zu Berlin, Invalidenstr. 42, 10115, Berlin, Germany.,Vitalant Research Institute, 270 Masonic Ave, San Francisco, CA, 94118, USA
| | - Robert-William Welke
- Institute for Biology, IRI Life Science, Humboldt-Universität zu Berlin, Invalidenstr. 42, 10115, Berlin, Germany
| | - Roberto Arturo Petazzi
- University of Potsdam, Institute of Biochemistry and Biology, Karl-Liebknecht-Str. 24-25, 14476, Potsdam, Germany
| | - Ronny Bergmann
- Institute for Biology, IRI Life Science, Humboldt-Universität zu Berlin, Invalidenstr. 42, 10115, Berlin, Germany
| | - Matthias Schade
- Institute for Biology, IRI Life Science, Humboldt-Universität zu Berlin, Invalidenstr. 42, 10115, Berlin, Germany
| | - Yechiel Shai
- Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot, Israel
| | - Salvatore Chiantia
- University of Potsdam, Institute of Biochemistry and Biology, Karl-Liebknecht-Str. 24-25, 14476, Potsdam, Germany
| | - Andreas Herrmann
- Institute for Biology, IRI Life Science, Humboldt-Universität zu Berlin, Invalidenstr. 42, 10115, Berlin, Germany.
| | - Roland Schwarzer
- Institute for Biology, IRI Life Science, Humboldt-Universität zu Berlin, Invalidenstr. 42, 10115, Berlin, Germany. .,Department of Biomolecular Sciences, Weizmann Institute of Science, Rehovot, Israel. .,Gladstone Institute of Virology and Immunology, 1650 Owens Street, San Francisco, CA, 95158, USA.
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2
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Evidence that Processing of the Severe Fever with Thrombocytopenia Syndrome Virus Gn/Gc Polyprotein Is Critical for Viral Infectivity and Requires an Internal Gc Signal Peptide. PLoS One 2016; 11:e0166013. [PMID: 27855227 PMCID: PMC5113920 DOI: 10.1371/journal.pone.0166013] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2016] [Accepted: 10/21/2016] [Indexed: 12/20/2022] Open
Abstract
The severe fever with thrombocytopenia syndrome virus (SFTSV) is an emerging, highly pathogenic bunyavirus against which neither antivirals nor vaccines are available. The SFTSV glycoproteins, Gn and Gc, facilitate viral entry into host cells. Gn and Gc are generated from a precursor protein, Gn/Gc, but it is currently unknown how the precursor is converted into the single proteins and whether this process is required for viral infectivity. Employing a rhabdoviral pseudotyping system, we demonstrate that a predicted signal sequence at the N-terminus of Gc is required for Gn/Gc processing and viral infectivity while potential proprotein convertase cleavage sites in Gc are dispensable. Moreover, we show that expression of Gn or Gc alone is not sufficient for host cell entry while particles bearing both proteins are infectious, and we provide evidence that Gn facilitates Golgi transport and virion incorporation of Gc. Collectively, these results suggest that signal peptidase liberates mature Gc from the Gn/Gc precursor and that this process is essential for viral infectivity and thus constitutes a potential target for antiviral intervention.
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3
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The Role of Phlebovirus Glycoproteins in Viral Entry, Assembly and Release. Viruses 2016; 8:v8070202. [PMID: 27455305 PMCID: PMC4974537 DOI: 10.3390/v8070202] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2016] [Revised: 07/13/2016] [Accepted: 07/14/2016] [Indexed: 01/08/2023] Open
Abstract
Bunyaviruses are enveloped viruses with a tripartite RNA genome that can pose a serious threat to animal and human health. Members of the Phlebovirus genus of the family Bunyaviridae are transmitted by mosquitos and ticks to humans and include highly pathogenic agents like Rift Valley fever virus (RVFV) and severe fever with thrombocytopenia syndrome virus (SFTSV) as well as viruses that do not cause disease in humans, like Uukuniemi virus (UUKV). Phleboviruses and other bunyaviruses use their envelope proteins, Gn and Gc, for entry into target cells and for assembly of progeny particles in infected cells. Thus, binding of Gn and Gc to cell surface factors promotes viral attachment and uptake into cells and exposure to endosomal low pH induces Gc-driven fusion of the viral and the vesicle membranes. Moreover, Gn and Gc facilitate virion incorporation of the viral genome via their intracellular domains and Gn and Gc interactions allow the formation of a highly ordered glycoprotein lattice on the virion surface. Studies conducted in the last decade provided important insights into the configuration of phlebovirus Gn and Gc proteins in the viral membrane, the cellular factors used by phleboviruses for entry and the mechanisms employed by phlebovirus Gc proteins for membrane fusion. Here, we will review our knowledge on the glycoprotein biogenesis and the role of Gn and Gc proteins in the phlebovirus replication cycle.
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4
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Hepojoki J, Strandin T, Lankinen H, Vaheri A. Hantavirus structure--molecular interactions behind the scene. J Gen Virol 2012; 93:1631-1644. [PMID: 22622328 DOI: 10.1099/vir.0.042218-0] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Viruses of the genus Hantavirus, carried and transmitted by rodents and insectivores, are the exception in the vector-borne virus family Bunyaviridae, since viruses of the other genera are transmitted via arthropods. The single-stranded, negative-sense, RNA genome of hantaviruses is trisegmented into small, medium and large (S, M and L) segments. The segments, respectively, encode three structural proteins: nucleocapsid (N) protein, two glycoproteins Gn and Gc and an RNA-dependent RNA-polymerase. The genome segments, encapsidated by the N protein to form ribonucleoproteins, are enclosed inside a lipid envelope that is decorated by spikes composed of Gn and Gc. The virion displays round or pleomorphic morphology with a diameter of roughly 120-160 nm depending on the detection method. This review focuses on the structural components of hantaviruses, their interactions, the mechanisms behind virion assembly and the interactions that maintain virion integrity. We attempt to summarize recent results on the virion structure and to suggest mechanisms on how the assembly is driven. We also compare hantaviruses to other bunyaviruses with known structure.
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Affiliation(s)
- Jussi Hepojoki
- Department of Virology, Peptide and Protein Laboratory, Infection Biology Research Program, Haartman Institute, University of Helsinki, Finland
| | - Tomas Strandin
- Department of Virology, Peptide and Protein Laboratory, Infection Biology Research Program, Haartman Institute, University of Helsinki, Finland
| | - Hilkka Lankinen
- Department of Virology, Peptide and Protein Laboratory, Infection Biology Research Program, Haartman Institute, University of Helsinki, Finland
| | - Antti Vaheri
- Department of Virology, Peptide and Protein Laboratory, Infection Biology Research Program, Haartman Institute, University of Helsinki, Finland
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Ribeiro D, Foresti O, Denecke J, Wellink J, Goldbach R, Kormelink RJM. Tomato spotted wilt virus glycoproteins induce the formation of endoplasmic reticulum- and Golgi-derived pleomorphic membrane structures in plant cells. J Gen Virol 2008; 89:1811-1818. [PMID: 18632951 DOI: 10.1099/vir.0.2008/001164-0] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2023] Open
Abstract
Tomato spotted wilt virus (TSWV) particles are spherical and enveloped, an uncommon feature among plant infecting viruses. Previous studies have shown that virus particle formation involves the enwrapment of ribonucleoproteins with viral glycoprotein containing Golgi stacks. In this study, the localization and behaviour of the viral glycoproteins Gn and Gc were analysed, upon transient expression in plant protoplasts. When separately expressed, Gc was solely observed in the endoplasmic reticulum (ER), whereas Gn was found both within the ER and Golgi membranes. Upon co-expression, both glycoproteins were found at ER-export sites and ultimately at the Golgi complex, confirming the ability of Gn to rescue Gc from the ER, possibly due to heterodimerization. Interestingly, both Gc and Gn were shown to induce the deformation of ER and Golgi membranes, respectively, also observed upon co-expression of the two glycoproteins. The behaviour of both glycoproteins within the plant cell and the phenomenon of membrane deformation are discussed in light of the natural process of viral infection.
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Affiliation(s)
- Daniela Ribeiro
- Wageningen University, Laboratory of Virology, Binnenhaven 11, 6709 PD Wageningen, The Netherlands
| | - Ombretta Foresti
- University of Leeds, Centre for Plant Sciences, Clarendon Way, Leeds LS2 9JT, UK
| | - Jurgen Denecke
- University of Leeds, Centre for Plant Sciences, Clarendon Way, Leeds LS2 9JT, UK
| | - Joan Wellink
- Wageningen University, Laboratory of Molecular Biology, Dreijenlaan 3, 6703 HA Wageningen, The Netherlands
| | - Rob Goldbach
- Wageningen University, Laboratory of Virology, Binnenhaven 11, 6709 PD Wageningen, The Netherlands
| | - Richard J M Kormelink
- Wageningen University, Laboratory of Virology, Binnenhaven 11, 6709 PD Wageningen, The Netherlands
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6
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Overby AK, Popov VL, Pettersson RF, Neve EPA. The cytoplasmic tails of Uukuniemi Virus (Bunyaviridae) G(N) and G(C) glycoproteins are important for intracellular targeting and the budding of virus-like particles. J Virol 2007; 81:11381-91. [PMID: 17670814 PMCID: PMC2045573 DOI: 10.1128/jvi.00767-07] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Functional motifs within the cytoplasmic tails of the two glycoproteins G(N) and G(C) of Uukuniemi virus (UUK) (Bunyaviridae family) were identified with the help of our recently developed virus-like particle (VLP) system for UUK virus (A. K. Overby, V. Popov, E. P. Neve, and R. F. Pettersson, J. Virol. 80:10428-10435, 2006). We previously reported that information necessary for the packaging of ribonucleoproteins into VLPs is located within the G(N) cytoplasmic tail (A. K. Overby, R. F. Pettersson, and E. P. Neve, J. Virol. 81:3198-3205, 2007). The G(N) glycoprotein cytoplasmic tail specifically interacts with the ribonucleoproteins and is critical for genome packaging. In addition, two other regions in the G(N) cytoplasmic tail, encompassing residues 21 to 25 and 46 to 50, were shown to be important for particle generation and release. By the introduction of point mutations within these two regions, we demonstrate that leucines at positions 23 and 24 are crucial for the initiation of VLP budding, while leucine 46, glutamate 47, and leucine 50 are important for efficient exit from the endoplasmic reticulum and subsequent transport to the Golgi complex. We found that budding and particle generation are highly dependent on the intracellular localization of both glycoproteins. The short cytoplasmic tail of UUK G(C) contains a lysine at position -3 from the C terminus that is highly conserved among members of the Phlebovirus, Hantavirus, and Orthobunyavirus genera. Mutating this single amino acid residue in G(C) resulted in the mislocalization of not only G(C) but also G(N) to the plasma membrane, and VLP generation was compromised in cells expressing this mutant. Together, these results demonstrate that the cytoplasmic tails of both G(N) and G(C) contain specific information necessary for efficient virus particle generation.
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Affiliation(s)
- Anna K Overby
- Ludwig Institute for Cancer Research, Stockholm Branch, Karolinska Institute, Box 240, SE-17177 Stockholm, Sweden
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7
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Overby AK, Popov V, Neve EPA, Pettersson RF. Generation and analysis of infectious virus-like particles of uukuniemi virus (bunyaviridae): a useful system for studying bunyaviral packaging and budding. J Virol 2006; 80:10428-35. [PMID: 16928751 PMCID: PMC1641803 DOI: 10.1128/jvi.01362-06] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In the present report we describe an infectious virus-like particle (VLP) system for the Uukuniemi (UUK) virus, a member of the Bunyaviridae family. It utilizes our recently developed reverse genetic system based on the RNA polymerase I minigenome system for UUK virus used to study replication, encapsidation, and transcription by monitoring reporter gene expression. Here, we have added the glycoprotein precursor expression plasmid together with the minigenome, nucleoprotein, and polymerase to generate VLPs, which incorporate the minigenome and are released into the supernatant. The particles are able to infect new cells, and reporter gene expression can be monitored if the trans-acting viral proteins (RNA polymerase and nucleoprotein) are also expressed in these cells. No minigenome transfer occurred in the absence of glycoproteins, demonstrating that the glycoproteins are absolutely required for the generation of infectious particles. Moreover, expression of glycoproteins alone was sufficient to produce and release VLPs. We show that the ribonucleoproteins (RNPs) are incorporated into VLPs but are not required for the generation of particles. Morphological analysis of the particles by electron microscopy revealed that VLPs, either with or without minigenomes, display a surface morphology indistinguishable from that of the authentic UUK virus and that they bud into Golgi vesicles in the same way as UUK virus does. This infectious VLP system will be very useful for studying the bunyaviral structural components required for budding and packaging of RNPs and receptor binding and may also be useful for the development of new vaccines for the human pathogens from this family.
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Affiliation(s)
- Anna K Overby
- Ludwig Institute for Cancer Research, Stockholm Branch, Karolinska Institute, Box 240, SE-17177 Stockholm, Sweden
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8
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Snippe M, Goldbach R, Kormelink R. Tomato spotted wilt virus particle assembly and the prospects of fluorescence microscopy to study protein-protein interactions involved. Adv Virus Res 2006; 65:63-120. [PMID: 16387194 DOI: 10.1016/s0065-3527(05)65003-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Affiliation(s)
- Marjolein Snippe
- Department of Asthma, Allergy, and Respiratory Diseases, King's College, London, WC2R 2LS United Kingdom
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9
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Shi X, Brauburger K, Elliott RM. Role of N-linked glycans on bunyamwera virus glycoproteins in intracellular trafficking, protein folding, and virus infectivity. J Virol 2005; 79:13725-34. [PMID: 16227292 PMCID: PMC1262612 DOI: 10.1128/jvi.79.21.13725-13734.2005] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The membrane glycoproteins (Gn and Gc) of Bunyamwera virus (BUN, family Bunyaviridae) contain three potential sites for the attachment of N-linked glycans: one site (N60) on Gn and two (N624 and N1169) on Gc. We determined that all three sites are glycosylated. Digestion of the glycoproteins with endo-beta-N-acetylglucosaminidase H (endo H) or peptide:N-glycosidase F revealed that Gn and Gc differ significantly in their glycan status and that late in infection Gc glycans remain endo H sensitive. The roles of the N-glycans in intracellular trafficking of the glycoproteins to the Golgi, protein folding, and virus replication were investigated by mutational analysis and confocal immunofluorescence. Elimination of the glycan on Gn, by changing N60 to a Q residue, resulted in the protein misfolding and failure of both Gn and Gc proteins to traffic to the Golgi complex. We were unable to rescue a viable virus by reverse genetics from a cDNA containing the N60Q mutation. In contrast, mutant Gc proteins lacking glycans on either N624 or N1169, or both sites, were able to target to the Golgi. Gc proteins containing mutations N624Q and N1169Q acquired endo H resistance. Three viable N glycosylation-site-deficient viruses, lacking glycans on one site or both sites on Gc, were created by reverse genetics. The viability of these recombinant viruses and analysis of growth kinetics indicates that the glycans on Gc are not essential for BUN replication, but they do contribute to the efficiency of virus infection.
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Affiliation(s)
- Xiaohong Shi
- Division of Virology, Institute of Virology, University of Glasgow, Church St., Glasgow G11 5JR, Scotland, United Kingdom
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10
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Abstract
Many viruses express membrane proteins. For enveloped viruses in particular, membrane proteins are frequently structural components of the virus that mediate the essential tasks of receptor recognition and membrane fusion. The functional activities of these proteins require that they are sorted correctly in infected cells. These sorting events often depend on the ability of the virus to mimic cellular protein trafficking signals and to interact with the cellular trafficking machinery. Importantly, loss or modification of these signals can influence virus infectivity and pathogenesis.
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Affiliation(s)
- R Byland
- MRC-LMCB and Department of Biochemistry and Molecular Biology, University College London, London, WC1E 6BT, UK
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11
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Novoa RR, Calderita G, Cabezas P, Elliott RM, Risco C. Key Golgi factors for structural and functional maturation of bunyamwera virus. J Virol 2005; 79:10852-63. [PMID: 16103138 PMCID: PMC1193595 DOI: 10.1128/jvi.79.17.10852-10863.2005] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Several complex enveloped viruses assemble in the membranes of the secretory pathway, such as the Golgi apparatus. Among them, bunyaviruses form immature viral particles that change their structure in a trans-Golgi-dependent manner. To identify key Golgi factors for viral structural maturation, we have purified and characterized the three viral forms assembled in infected cells, two intracellular intermediates and the extracellular mature virion. The first viral form is a pleomorphic structure with fully endo-beta-N-acetylglucosaminidase H (Endo-H)-sensitive, nonsialylated glycoproteins. The second viral intermediate is a structure with hexagonal and pentagonal contours and partially Endo-H-resistant glycoproteins. Sialic acid is incorporated into the small glycoprotein of this second viral form. Growing the virus in glycosylation-deficient cells confirmed that acquisition of Endo-H resistance but not sialylation is critical for the trans-Golgi-dependent structural maturation and release of mature viruses. Conformational changes in viral glycoproteins triggered by changes in sugar composition would then induce the assembly of a compact viral particle of angular contours. These structures would be competent for the second maturation step, taking place during exit from cells, that originates fully infectious virions.
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Affiliation(s)
- Reyes R Novoa
- Department of Structure of Macromolecules, Centro Nacional de Biotecnología, CSIC, Cantoblanco, Madrid, Spain
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12
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Gerrard SR, Nichol ST. Characterization of the Golgi retention motif of Rift Valley fever virus G(N) glycoprotein. J Virol 2002; 76:12200-10. [PMID: 12414959 PMCID: PMC136907 DOI: 10.1128/jvi.76.23.12200-12210.2002] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
As Rift Valley fever (RVF) virus, and probably all members of the family Bunyaviridae, matures in the Golgi apparatus, the targeting of the virus glycoproteins to the Golgi apparatus plays a pivotal role in the virus replication cycle. No consensus Golgi localization motif appears to be shared among the glycoproteins of these viruses. The viruses of the family Bunyaviridae synthesize their glycoproteins, G(N) and G(C), as a polyprotein. The Golgi localization signal of RVF virus has been shown to reside within the G(N) protein by use of a plasmid-based transient expression system to synthesize individual G(N) and G(C) proteins. While the distribution of individually expressed G(N) significantly overlaps with cellular Golgi proteins such as beta-COP and GS-28, G(C) expressed in the absence of G(N) localizes to the endoplasmic reticulum. Further analysis of expressed G(N) truncated proteins and green fluorescent protein/G(N) chimeric proteins demonstrated that the RVF virus Golgi localization signal mapped to a 48-amino-acid region of G(N) encompassing the 20-amino-acid transmembrane domain and the adjacent 28 amino acids of the cytosolic tail.
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Affiliation(s)
- Sonja R Gerrard
- Special Pathogens Branch, Division of Viral and Rickettsial Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia 30333, USA
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13
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Flick R, Pettersson RF. Reverse genetics system for Uukuniemi virus (Bunyaviridae): RNA polymerase I-catalyzed expression of chimeric viral RNAs. J Virol 2001; 75:1643-55. [PMID: 11160662 PMCID: PMC114073 DOI: 10.1128/jvi.75.4.1643-1655.2001] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2000] [Accepted: 11/07/2000] [Indexed: 12/28/2022] Open
Abstract
We describe here the development of a reverse genetics system for the phlebovirus Uukuniemi virus, a member of the Bunyaviridae family, by using RNA polymerase I (pol I)-mediated transcription. Complementary DNAs containing the coding sequence for either chloramphenicol acetyltransferase (CAT) or green fluorescent protein (GFP) (both in antisense orientation) were flanked by the 5'- and 3'-terminal untranslated regions of the Uukuniemi virus sense or complementary RNA derived from the medium-sized (M) RNA segment. This chimeric cDNA (pol I expression cassette) was cloned between the murine pol I promoter and terminator and the plasmid transfected into BHK-21 cells. When such cells were either superinfected with Uukuniemi virus or cotransfected with expression plasmids encoding the L (RNA polymerase), N (nucleoprotein), and NSs (nonstructural protein) viral proteins, strong CAT activity or GFP expression was observed. CAT activity was consistently stronger in cells expressing L plus N than following superinfection. No activity was seen without superinfection, nor was activity detected when either the L or N expression plasmid was omitted. Omitting NSs expression had no effect on CAT activity or GFP expression, indicating that this protein is not needed for viral RNA replication or transcription. CAT activity could be serially passaged to fresh cultures by transferring medium from CAT-expressing cells, indicating that recombinant virus containing the reporter construct had been produced. In summary, we demonstrate that the RNA pol I system, originally developed for influenza virus, which replicates in the nucleus, has strong potential for the development of an efficient reverse genetics system also for Bunyaviridae members, which replicate in the cytoplasm.
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Affiliation(s)
- R Flick
- Ludwig Institute for Cancer Research, Stockholm Branch, Karolinska Institute, S-17177 Stockholm, Sweden
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14
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Kikkert M, Verschoor A, Kormelink R, Rottier P, Goldbach R. Tomato spotted wilt virus glycoproteins exhibit trafficking and localization signals that are functional in mammalian cells. J Virol 2001; 75:1004-12. [PMID: 11134314 PMCID: PMC113997 DOI: 10.1128/jvi.75.2.1004-1012.2001] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The glycoprotein precursor (G1/G2) gene of tomato spotted wilt virus (TSWV) was expressed in BHK cells using the Semliki Forest virus expression system. The results reveal that in this cell system, the precursor is efficiently cleaved and the resulting G1 and G2 glycoproteins are transported from the endoplasmic reticulum (ER) to the Golgi complex, where they are retained, a process that could be blocked by tunicamycin. Expression of G2 alone resulted in transport to and retention in the Golgi complex, albeit less efficient, suggesting that G2 contains a Golgi retention signal. G1 alone was retained in the ER, irrespective of whether it contained the precursor's signal sequence or its own N-terminal hydrophobic sequence. Coexpression of G1 and G2 from separate gene constructs resulted in rescue of efficient G1 transport, as the proteins coaccumulated in the Golgi complex, indicating that their interaction is essential for proper targeting to this organelle. The results demonstrate that transport and targeting of the plant TSWV glycoproteins in mammalian BHK cells are strikingly similar to those of animal-infecting bunyavirus glycoproteins in mammalian cells. The observations are likely to reflect the dual tropism of TSWV, which replicates both in its plant host and in its animal (thrips) vector.
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Affiliation(s)
- M Kikkert
- Laboratory of Virology, Wageningen University, Wageningen, The Netherlands
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15
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Veijola J, Pettersson RF. Transient association of calnexin and calreticulin with newly synthesized G1 and G2 glycoproteins of uukuniemi virus (family Bunyaviridae). J Virol 1999; 73:6123-7. [PMID: 10364370 PMCID: PMC112679 DOI: 10.1128/jvi.73.7.6123-6127.1999] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The membrane glycoproteins G1 and G2 of Uukuniemi virus, a member of the Bunyaviridae family, are cotranslationally cleaved from a common precursor in the endoplasmic reticulum (ER). Here, we show that newly made G1 and G2 associate transiently with calnexin and calreticulin, two lectins involved in glycoprotein folding in the ER. Stable complexes between G1-G2 and calnexin or calreticulin could be immunoprecipitated after solubilization of virus-infected BHK21 cells with the detergents digitonin or Triton X-100. In addition, G1-G2-calnexin complexes could be recovered after solubilization with CHAPS (3-[(3-cholamidopropyl)-dimethylammonio]-1-propane sulfonate), while G1-G2-calreticulin complexes were not readily detected by using this detergent. Only endoglycosidase H-sensitive forms of G1 were found complexed with calnexin. Pulse-chase experiments showed that G1 and G2 associated with both chaperones transiently for up to 120 min. Sequential immunoprecipitations with anticalreticulin and anticalnexin antisera indicated that about 50% of newly synthesized G1 and G2 was associated with either calnexin or calreticulin. Our previous results have shown that newly synthesized G1 and G2 transiently interact also with the ER chaperone BiP and with protein disulfide isomerase (R. Persson and R. F. Pettersson, J. Cell Biol. 112:257-266, 1991). Taking all of this into consideration, we conclude that the folding of G1 and G2 in the ER is catalyzed by at least four different folding factors.
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Affiliation(s)
- J Veijola
- Ludwig Institute for Cancer Research, Stockholm Branch, Karolinska Institute, S-17177 Stockholm, Sweden
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16
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Andersson AM, Pettersson RF. Targeting of a short peptide derived from the cytoplasmic tail of the G1 membrane glycoprotein of Uukuniemi virus (Bunyaviridae) to the Golgi complex. J Virol 1998; 72:9585-96. [PMID: 9811692 PMCID: PMC110468 DOI: 10.1128/jvi.72.12.9585-9596.1998] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Members of the Bunyaviridae family acquire an envelope by budding through the lipid bilayer of the Golgi complex. The budding compartment is thought to be determined by the accumulation of the two heterodimeric membrane glycoproteins G1 and G2 in the Golgi. We recently mapped the retention signal for Golgi localization in one Bunyaviridae member (Uukuniemi virus) to the cytoplasmic tail of G1. We now show that a myc-tagged 81-residue G1 tail peptide expressed in BHK21 cells is efficiently targeted to the Golgi complex and retained there during a 3-h chase. Green-fluorescence protein tagged at either end with this peptide or with a C-terminally truncated 60-residue G1 tail peptide was also efficiently targeted to the Golgi. The 81-residue peptide colocalized with mannosidase II (a medial Golgi marker) and partially with p58 (an intermediate compartment marker) and TGN38 (a trans-Golgi marker). In addition, the 81-residue tail peptide induced the formation of brefeldin A-resistant vacuoles that did not costain with markers for other membrane compartments. Removal of the first 10 N-terminal residues had no effect on the Golgi localization but abolished the vacuolar staining. The shortest peptide still able to become targeted to the Golgi encompassed residues 10 to 40. Subcellular fractionation showed that the 81-residue tail peptide was associated with microsomal membranes. Removal of the two palmitylation sites from the tail peptide did not affect Golgi localization and had only a minor effect on the association with microsomal membranes. Taken together, the results provide strong evidence that Golgi retention of the heterodimeric G1-G2 spike protein complex of Uukuniemi virus is mediated by a short region in the cytoplasmic tail of the G1 glycoprotein.
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Affiliation(s)
- A M Andersson
- Ludwig Institute for Cancer Research, Stockholm Branch, Karolinska Institute, S-17177 Stockholm, Sweden
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Alconada A, Bauer U, Baudoux L, Piette J, Hoflack B. Intracellular transport of the glycoproteins gE and gI of the varicella-zoster virus. gE accelerates the maturation of gI and determines its accumulation in the trans-Golgi network. J Biol Chem 1998; 273:13430-6. [PMID: 9593675 DOI: 10.1074/jbc.273.22.13430] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The varicella-zoster virus (VZV) is the etiological agent of two different human pathologies, chickenpox (varicella) and shingles (zoster). This alphaherpesvirus is believed to acquire its lipidic envelope in the trans-Golgi network (TGN). This is consistent with previous data showing that the most abundant VZV envelope glycoprotein gE accumulates at steady-state in this organelle when expressed from cloned cDNA. In the present study, we have investigated the intracellular trafficking of gI, another VZV envelope glycoprotein. In transfected cells, this protein shows a very slow biosynthetic transport to the cell surface where it accumulates. However, upon co-expression of gE, gI experiences a dramatic increase in its exit rate from the endoplasmic reticulum, it accumulates in a sialyltransferase-positive compartment, presumably the TGN, and cycles between this compartment and the cell surface. This differential behavior results from the ability of gE and gI to form a complex in the early stages of the biosynthetic pathway whose intracellular traffic is exclusively determined by the sorting information in the tail of gE. Thus, gI provides the first example of a molecule localized to the TGN by means of its association with another TGN protein. We also show that, during the early stages of VZV infection, both proteins are also found in the TGN of the host cell. This suggests the existence of an intermediate stage during VZV biogenesis in which the envelope glycoproteins, transiently arrested in the TGN, could promote the envelopment of newly synthesized nucleocapsids into this compartment and, therefore, the assembly of infective viruses.
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Affiliation(s)
- A Alconada
- Institut de Biologie de Lille (IFR3), Institut Pasteur de Lille, 59021 Lille, France
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Andersson AM, Melin L, Bean A, Pettersson RF. A retention signal necessary and sufficient for Golgi localization maps to the cytoplasmic tail of a Bunyaviridae (Uukuniemi virus) membrane glycoprotein. J Virol 1997; 71:4717-27. [PMID: 9151865 PMCID: PMC191693 DOI: 10.1128/jvi.71.6.4717-4727.1997] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Members of the Bunyaviridae family mature by a budding process in the Golgi complex. The site of maturation is thought to be largely determined by the accumulation of the two spike glycoproteins, G1 and G2, in this organelle. Here we show that the signal for localizing the Uukuniemi virus (a phlebovirus) spike protein complex to the Golgi complex resides in the cytoplasmic tail of G1. We constructed chimeric proteins in which the ectodomain, transmembrane domain (TMD), and cytoplasmic tail (CT) of Uukuniemi virus G1 were exchanged with the corresponding domains of either vesicular stomatitis virus G protein (VSV G), chicken lysozyme, or CD4, all proteins readily transported to the plasma membrane. The chimeras were expressed in HeLa or BHK-21 cells by using either the T7 RNA polymerase-driven vaccinia virus system or the Semliki Forest virus system. The fate of the chimeric proteins was monitored by indirect immunofluorescence, and their localizations were compared by double labeling with markers specific for the Golgi complex. The results showed that the ectodomain and TMD (including the 10 flanking residues on either side of the membrane) of G1 played no apparent role in targeting chimeric proteins to the Golgi complex. Instead, all chimeras containing the CT of G1 were efficiently targeted to the Golgi complex and colocalized with mannosidase II, a Golgi-specific enzyme. Conversely, replacing the CT of G1 with that from VSV G resulted in the efficient transport of the chimeric protein to the cell surface. Progressive deletions of the G1 tail suggested that the Golgi retention signal maps to a region encompassing approximately residues 10 to 50, counting from the proposed border between the TMD and the tail. Both G1 and G2 were found to be acylated, as shown by incorporation of [3H]palmitate into the viral proteins. By mutational analyses of CD4-G1 chimeras, the sites for palmitylation were mapped to two closely spaced cysteine residues in the G1 tail. Changing either or both of these cysteines to alanine had no effect on the targeting of the chimeric protein to the Golgi complex.
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Affiliation(s)
- A M Andersson
- Ludwig Institute for Cancer Research, Stockholm Branch, Sweden
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19
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Jäntti J, Hildén P, Rönkä H, Mäkiranta V, Keränen S, Kuismanen E. Immunocytochemical analysis of Uukuniemi virus budding compartments: role of the intermediate compartment and the Golgi stack in virus maturation. J Virol 1997; 71:1162-72. [PMID: 8995638 PMCID: PMC191169 DOI: 10.1128/jvi.71.2.1162-1172.1997] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Previous studies have suggested that Uukuniemi virus, a bunyavirus, matures at the membranes of the Golgi complex. In this study we have employed immunocytochemical techniques to analyze in detail the budding compartment(s) of the virus. Electron microscopy of infected BHK-21 cells showed that virus particles are found in the cisternae throughout the Golgi stack. Within the cisternae, the virus particles were located preferentially in the dilated rims. This would suggest that virus budding may begin at or before the cis Golgi membranes. The virus budding compartment was studied further by immunoelectron microscopy with a pre-Golgi intermediate compartment marker, p58, and a Golgi stack marker protein, mannosidase II (ManII). Virus particles and budding virus were detected in ManII-positive Golgi stack membranes and, interestingly, in both juxtanuclear and peripheral p58-positive elements of the intermediate compartment. In cells incubated at 15 degrees C the nucleocapsid and virus envelope proteins were seen to accumulate in the intermediate compartment. Immunoelectron microscopy demonstrated that at 15 degrees C the nucleocapsid is associated with membranes that show a characteristic distribution and tubulo-vesicular morphology of the pre-Golgi intermediate compartment. These membranes contained virus particles in the lumen. The results indicate that the first site of formation of Uukuniemi virus particles is the pre-Golgi intermediate compartment and that virus budding continues in the Golgi stack. The results raise questions about the intracellular transport pathway of the virus particles, which are 100 to 120 nm in diameter and are therefore too large to be transported in the 60-nm-diameter vesicles postulated to function in the intra-Golgi transport. The distribution of the virus in the Golgi stack may imply that the cisternae themselves have a role in the vectorial transport of virus particles.
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Affiliation(s)
- J Jäntti
- Department of Biosciences, University of Helsinki Biocenter, Finland
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Rwambo PM, Shaw MK, Rurangirwa FR, DeMartini JC. Ultrastructural studies on the replication and morphogenesis of Nairobi sheep disease virus, a Nairovirus. Arch Virol 1996; 141:1479-92. [PMID: 8856028 DOI: 10.1007/bf01718249] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The Nairovirus Nairobi sheep disease virus (NSDV) affects sheep and goats causing severe hemorrhagic gastroenteritis and high mortality. Replication and morphogenesis of NSDV was determined by electron microscopic examination of ultra-thin sections of 143B and BHK-21 cells at varying times after infection. By 4 h post-infection (p.i.) of 143B cells, virions budding from the luminal side of the bilayer membrane of smooth membrane vesicles were observed. Morphologically mature virus particles were electron-dense, spherical and of uniform size (100 nm diameter) and accumulated in smooth membrane vesicles associated with the Golgi complex. In BHK-21 clone 13 cells, mature virus particles in smooth membrane vesicles were present by 8 h p.i. The morphogenesis of NSDV was restricted to the smooth membrane vesicles of Golgi complex, and budding of virus from other sites was not detected. Extracellular virus particles were observed by 10 h p.i., before expression of cytopathic effects. The cytopathic effects were observed at 24 h p.i. in 143B cells and at 36 h p.i. in BHK-21 cells. The morphology and morphogenesis of NSDV in BHK-21 cells and in 143B cells resembles that of other members of the family Bunyaviridae.
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Affiliation(s)
- P M Rwambo
- Small Ruminant Collaborative Research Support Program (SR-CRSP), Kenya Agricultural Research Institute
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Estabrook EM, Suyenaga K, Tsai JH, Falk BW. Maize stripe tenuivirus RNA2 transcripts in plant and insect hosts and analysis of pvc2, a protein similar to the Phlebovirus virion membrane glycoproteins. Virus Genes 1996; 12:239-47. [PMID: 8883361 DOI: 10.1007/bf00284644] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The complete sequence of the maize stripe tenuivirus (MStV) RNA2 was determined (3337 nucleotides). RNA2 contains two large open reading frames (ORFs) arranged in an ambisense orientation and specific RNAs of ca. 700 and 2600 nucleotides corresponding to the ORFs were detected in MStV-infected plants and planthoppers. The deduced amino acid sequence of the 23,500 MW protein (pv2) encoded by viral RNA2 (vRNA2) was similar to proteins encoded by the rice stripe (RStV) and rice hoja blanca tenuiviruses vRNA2. Sequence analysis suggested that pv2 is membrane associated. The 93,900 MW protein (pvc2) encoded by viral complementary MStV RNA2 (vcRNA2) was similar to the 94,000 MW protein of RStV RNA2 and to the virion membrane glycoproteins for Phlebovirus members of the Bunyaviridae. The phlebovirus glycoprotein cleavage site was similar to a region in the MStV and RStV proteins suggesting that the tenuivirus pvc2 may be processed analogous to the phlebovirus glycoproteins.
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Affiliation(s)
- E M Estabrook
- Department of Plant Pathology, University of California, Davis 95616, USA.
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Melin L, Persson R, Andersson A, Bergström A, Rönnholm R, Pettersson RF. The membrane glycoprotein G1 of Uukuniemi virus contains a signal for localization to the Golgi complex. Virus Res 1995; 36:49-66. [PMID: 7625126 PMCID: PMC7133855 DOI: 10.1016/0168-1702(95)00006-c] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Members of the Bunyaviridae family acquire their envelopes by budding into the Golgi complex (GC). The accumulation of the membrane glycoproteins G1 and G2 in the GC probably determines the site of maturation. Here we have studied the intracellular transport and targeting to the GC of G1 and G2 of Uukuniemi virus, a member of the Phlebovirus genus, and report on their expression from cloned cDNAs either together or separately by using a T7 RNA polymerase-driven vaccinia virus expression system. When G1 and G2 were expressed together from a full-length cDNA as the p110 precursor, both proteins were localized to the Golgi complex, as evidenced by colocalization with the Golgi marker enzyme mannosidase II. Immunofluorescent staining indicated that G1 expressed alone also localized to the GC. However, pulse-chase experiments showed that G1 remained endoglycosidase H sensitive. G2 expressed alone remained associated with the endoplasmic reticulum (ER). G2 could be rescued from the ER and transported to the GC by coexpression with G1 from separate mRNAs. Coexpression also increased the efficiency of G1 transport to the GC. With none of the constructs could the glycoproteins be observed on the cell surface. These results show that efficient export of G1 and G2 from the ER requires coexpression of both proteins, in conformity with our previous results showing that G1 and G2 form heterodimeric complexes in the ER. Since G1 expressed alone is retained in the GC, we conclude that G1 contains a retention signal for localization to the GC. G2 might thus become associated with the GC indirectly via its interaction with G1.
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Affiliation(s)
- L Melin
- Ludwig Institute for Cancer Research, Stockholm, Sweden
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Abstract
Certain enveloped viruses are known to assemble on membranes of the Golgi complex. Intracellular budding is facilitated by targeting of the viral glycoproteins to this organelle. It is likely that these viral glycoproteins are retained in the Golgi by the same means as are endogenous Golgi proteins. Consequently, the study of Golgi-specific viral proteins has provided important clues to the nature of Golgi retention signals.
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Affiliation(s)
- T C Hobman
- Division of Cellular and Molecular Medicine, University of California, San Diego, La Jolla 92093-0651
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