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Arnold MM, Dijk A, López S. Double‐stranded RNA Viruses. Virology 2021. [DOI: 10.1002/9781119818526.ch2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Cell Entry-Independent Role for the Reovirus μ1 Protein in Regulating Necroptosis and the Accumulation of Viral Gene Products. J Virol 2019; 93:JVI.00199-19. [PMID: 30894465 DOI: 10.1128/jvi.00199-19] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2019] [Accepted: 03/13/2019] [Indexed: 12/14/2022] Open
Abstract
The reovirus outer capsid protein μ1 regulates cell death in infected cells. To distinguish between the roles of incoming, capsid-associated, and newly synthesized μ1, we used small interfering RNA (siRNA)-mediated knockdown. Loss of newly synthesized μ1 protein does not affect apoptotic cell death in HeLa cells but enhances necroptosis in L929 cells. Knockdown of μ1 also affects aspects of viral replication. We found that, while μ1 knockdown results in diminished release of infectious viral progeny from infected cells, viral minus-strand RNA, plus-strand RNA, and proteins that are not targeted by the μ1 siRNA accumulate to a greater extent than in control siRNA-treated cells. Furthermore, we observed a decrease in sensitivity of these viral products to inhibition by guanidine hydrochloride (GuHCl) (which targets minus-strand synthesis to produce double-stranded RNA) when μ1 is knocked down. Following μ1 knockdown, cell death is also less sensitive to treatment with GuHCl. Our studies suggest that the absence of μ1 allows enhanced transcriptional activity of newly synthesized cores and the consequent accumulation of viral gene products. We speculate that enhanced accumulation and detection of these gene products due to μ1 knockdown potentiates receptor-interacting protein 3 (RIP3)-dependent cell death.IMPORTANCE We used mammalian reovirus as a model to study how virus infections result in cell death. Here, we sought to determine how viral factors regulate cell death. Our work highlights a previously unknown role for the reovirus outer capsid protein μ1 in limiting the induction of a necrotic form of cell death called necroptosis. Induction of cell death by necroptosis requires the detection of viral gene products late in infection; μ1 limits cell death by this mechanism because it prevents excessive accumulation of viral gene products that trigger cell death.
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Reovirus Nonstructural Protein σNS Acts as an RNA Stability Factor Promoting Viral Genome Replication. J Virol 2018; 92:JVI.00563-18. [PMID: 29769334 DOI: 10.1128/jvi.00563-18] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2018] [Accepted: 05/07/2018] [Indexed: 12/23/2022] Open
Abstract
Viral nonstructural proteins, which are not packaged into virions, are essential for the replication of most viruses. Reovirus, a nonenveloped, double-stranded RNA (dsRNA) virus, encodes three nonstructural proteins that are required for viral replication and dissemination in the host. The reovirus nonstructural protein σNS is a single-stranded RNA (ssRNA)-binding protein that must be expressed in infected cells for production of viral progeny. However, the activities of σNS during individual steps of the reovirus replication cycle are poorly understood. We explored the function of σNS by disrupting its expression during infection using cells expressing a small interfering RNA (siRNA) targeting the σNS-encoding S3 gene and found that σNS is required for viral genome replication. Using complementary biochemical assays, we determined that σNS forms complexes with viral and nonviral RNAs. We also discovered, using in vitro and cell-based RNA degradation experiments, that σNS increases the RNA half-life. Cryo-electron microscopy revealed that σNS and ssRNAs organize into long, filamentous structures. Collectively, our findings indicate that σNS functions as an RNA-binding protein that increases the viral RNA half-life. These results suggest that σNS forms RNA-protein complexes in preparation for genome replication.IMPORTANCE Following infection, viruses synthesize nonstructural proteins that mediate viral replication and promote dissemination. Viruses from the family Reoviridae encode nonstructural proteins that are required for the formation of progeny viruses. Although nonstructural proteins of different viruses in the family Reoviridae diverge in primary sequence, they are functionally homologous and appear to facilitate conserved mechanisms of dsRNA virus replication. Using in vitro and cell culture approaches, we found that the mammalian reovirus nonstructural protein σNS binds and stabilizes viral RNA and is required for genome synthesis. This work contributes new knowledge about basic mechanisms of dsRNA virus replication and provides a foundation for future studies to determine how viruses in the family Reoviridae assort and replicate their genomes.
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Boyce M, McCrae MA, Boyce P, Kim JT. Inter-segment complementarity in orbiviruses: a driver for co-ordinated genome packaging in the Reoviridae? J Gen Virol 2016; 97:1145-1157. [PMID: 26763979 DOI: 10.1099/jgv.0.000400] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The process by which eukaryotic viruses with segmented genomes select a complete set of genome segments for packaging into progeny virus particles is not understood. In this study a model based on the association of genome segments through specific RNA-RNA interactions driven by base pairing was formalized and tested in the Orbivirus genus of the Reoviridae family. A strategy combining screening of the genomic sequences for inter-segment complementarity with direct functional testing of inter-segment RNA-RNA interactions using reverse genetics is described in the type species of the Orbivirus genus, Bluetongue virus (BTV). Two examples, involving four of the ten BTV genomic segments, of specific inter-segment interaction motifs whose maintenance is essential for the generation of infectious virus, were identified. Equivalent inter-segment complementarities were found between the identified regions of the orthologous genome segments of all orbiviruses, including phylogenetically distant species. Specific interaction of the participating RNA segments was confirmed in vitro using electrophoretic mobility shift assays, with the interactions inhibited using oligonucleotides complementary to the interaction motif of one of the interacting partners, and also through mutagenesis of the motifs. In each example, the base pairing rather than the absolute sequence was critical to the formation of a functional inter-segment interaction, with mutations only being tolerated in rescued virus if compensating changes were made in the interacting partner to restore uninterrupted base pairing. The absolute sequence of the complementarity motifs varied between species, indicating that this newly identified phenomenon may contribute to the observed lack of reassortment between Orbivirus species.
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Affiliation(s)
- Mark Boyce
- The Pirbright Institute, Pirbright, Woking GU24 0NF, UK
| | | | - Paul Boyce
- Mott MacDonald, Mott MacDonald House, 8-10 Sydenham Road, Croydon, CR0 2EE
| | - Jan T Kim
- The Pirbright Institute, Pirbright, Woking GU24 0NF, UK
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Abstract
Most viruses that replicate in the cytoplasm of host cells form neo-organelles that serve as sites of viral genome replication and particle assembly. These highly specialized structures concentrate viral replication proteins and nucleic acids, prevent the activation of cell-intrinsic defenses, and coordinate the release of progeny particles. Despite the importance of inclusion complexes in viral replication, there are key gaps in the knowledge of how these organelles form and mediate their functions. Reoviruses are nonenveloped, double-stranded RNA (dsRNA) viruses that serve as tractable experimental models for studies of dsRNA virus replication and pathogenesis. Following reovirus entry into cells, replication occurs in large cytoplasmic structures termed inclusions that fill with progeny virions. Reovirus inclusions are nucleated by viral nonstructural proteins, which in turn recruit viral structural proteins for genome replication and particle assembly. Components of reovirus inclusions are poorly understood, but these structures are generally thought to be devoid of membranes. We used transmission electron microscopy and three-dimensional image reconstructions to visualize reovirus inclusions in infected cells. These studies revealed that reovirus inclusions form within a membranous network. Viral inclusions contain filled and empty viral particles and microtubules and appose mitochondria and rough endoplasmic reticulum (RER). Immunofluorescence confocal microscopy analysis demonstrated that markers of the ER and ER-Golgi intermediate compartment (ERGIC) codistribute with inclusions during infection, as does dsRNA. dsRNA colocalizes with the viral protein σNS and an ERGIC marker inside inclusions. These findings suggest that cell membranes within reovirus inclusions form a scaffold to coordinate viral replication and assembly. Viruses alter the architecture of host cells to form an intracellular environment conducive to viral replication. This step in viral infection requires the concerted action of viral and host components and is potentially vulnerable to pharmacological intervention. Reoviruses form large cytoplasmic replication sites called inclusions, which have been described as membrane-free structures. Despite the importance of inclusions in the reovirus replication cycle, little is known about their formation and composition. We used light and electron microscopy to demonstrate that reovirus inclusions are membrane-containing structures and that the endoplasmic reticulum (ER) and the ER-Golgi intermediate compartment interact closely with these viral organelles. These findings enhance our understanding of the cellular machinery usurped by viruses to form inclusion organelles and complete an infectious cycle. This information, in turn, may foster the development of antiviral drugs that impede this essential viral replication step.
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Reovirus replication protein μ2 influences cell tropism by promoting particle assembly within viral inclusions. J Virol 2012; 86:10979-87. [PMID: 22837214 DOI: 10.1128/jvi.01172-12] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The double-stranded RNA virus mammalian reovirus displays broad cell, tissue, and host tropism. A critical checkpoint in the reovirus replication cycle resides within viral cytoplasmic inclusions, which are biosynthetic centers of genome multiplication and new-particle assembly. Replication of strain type 3 Dearing (T3) is arrested in Madin-Darby canine kidney (MDCK) cells at a step subsequent to inclusion development and prior to formation of genomic double-stranded RNA. This phenotype is primarily regulated by viral replication protein μ2. To understand how reovirus inclusions differ in productively and abortively infected MDCK cells, we used confocal immunofluorescence and thin-section transmission electron microscopy (TEM) to probe inclusion organization and particle morphogenesis. Although no abnormalities in inclusion morphology or viral protein localization were observed in T3-infected MDCK cells using confocal microscopy, TEM revealed markedly diminished production of mature progeny virions. T3 inclusions were less frequent and smaller than those formed by T3-T1M1, a productively replicating reovirus strain, and contained decreased numbers of complete particles. T3 replication was enhanced when cells were cultivated at 31°C, and inclusion ultrastructure at low-temperature infection more closely resembled that of a productive infection. These results indicate that particle assembly in T3-infected MDCK cells is defective, possibly due to a temperature-sensitive structural or functional property of μ2. Thus, reovirus cell tropism can be governed by interactions between viral replication proteins and the unique cell environment that modulate efficiency of particle assembly.
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Localization of mammalian orthoreovirus proteins to cytoplasmic factory-like structures via nonoverlapping regions of microNS. J Virol 2009; 84:867-82. [PMID: 19889754 DOI: 10.1128/jvi.01571-09] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Virally induced structures called viral factories form throughout the cytoplasm of cells infected with mammalian orthoreoviruses (MRV). When expressed alone in cells, MRV nonstructural protein microNS forms factory-like structures very similar in appearance to viral factories, suggesting that it is involved in forming the structural matrix of these structures. microNS also associates with MRV core particles; the core proteins mu2, lambda1, lambda2, lambda3, and sigma2; and the RNA-binding nonstructural protein sigmaNS. These multiple associations result in the recruitment or retention of these viral proteins or particles at factory-like structures. In this study, we identified the regions of microNS necessary and sufficient for these associations and additionally examined the localization of viral RNA synthesis in infected cells. We found that short regions within the amino-terminal 220 residues of microNS are necessary for associations with core particles and necessary and sufficient for associations with the proteins mu2, lambda1, lambda2, sigma2, and sigmaNS. We also found that only the lambda3 protein associates with the carboxyl-terminal one-third of microNS and that viral RNA is synthesized within viral factories. These results suggest that microNS may act as a cytoplasmic scaffolding protein involved in localizing and coordinating viral replication or assembly intermediates for the efficient production of progeny core particles during MRV infection.
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Ji WT, Chulu JL, Lin FL, Li SK, Lee LH, Liu HJ. Suppression of protein expression of three avian reovirus S-class genome segments by RNA interference. Vet Microbiol 2008; 129:252-61. [DOI: 10.1016/j.vetmic.2007.11.025] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2007] [Revised: 11/10/2007] [Accepted: 11/21/2007] [Indexed: 10/22/2022]
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Holm GH, Zurney J, Tumilasci V, Leveille S, Danthi P, Hiscott J, Sherry B, Dermody TS. Retinoic acid-inducible gene-I and interferon-beta promoter stimulator-1 augment proapoptotic responses following mammalian reovirus infection via interferon regulatory factor-3. J Biol Chem 2007; 282:21953-61. [PMID: 17540767 DOI: 10.1074/jbc.m702112200] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
During viral infection, cells initiate antiviral responses to contain replication and inhibit virus spread. One protective mechanism involves activation of transcription factors interferon regulatory factor-3 (IRF-3) and NF-kappaB, resulting in secretion of the antiviral cytokine, interferon-beta. Another is induction of apoptosis, killing the host cell before virus disseminates. Mammalian reovirus induces both interferon-beta and apoptosis, raising the possibility that both pathways are initiated by a common cellular sensor. We show here that reovirus activates IRF-3 with kinetics that parallel the activation of NF-kappaB, a known mediator of reovirus-induced apoptosis. Activation of IRF-3 requires functional retinoic acid inducible gene-I and interferon-beta promoter stimulator-1, but these intracellular sensors are dispensable for activation of NF-kappaB. Interferon-beta promoter stimulator-1 and IRF-3 are required for efficient apoptosis following reovirus infection, suggesting a common mechanism of antiviral cytokine induction and activation of the cell death response.
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Affiliation(s)
- Geoffrey H Holm
- Department of Pediatrics, Vanderbilt University School of Medicine, Nashville, TN 37232-2581, USA
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10
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Kobayashi T, Chappell JD, Danthi P, Dermody TS. Gene-specific inhibition of reovirus replication by RNA interference. J Virol 2006; 80:9053-63. [PMID: 16940517 PMCID: PMC1563907 DOI: 10.1128/jvi.00276-06] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2006] [Accepted: 07/03/2006] [Indexed: 01/26/2023] Open
Abstract
Mammalian reoviruses contain a genome of 10 segments of double-stranded RNA (dsRNA). Reovirus replication and assembly occur within distinct structures called viral inclusions, which form in the cytoplasm of infected cells. Viral nonstructural proteins muNS and sigmaNS and core protein mu2 play key roles in forming viral inclusions and recruiting other viral proteins and RNA to these structures for replication and assembly. However, the precise functions of these proteins in viral replication are poorly defined. Therefore, to better understand the functions of reovirus proteins associated with formation of viral inclusions, we used plasmid-based vectors to establish 293T cell lines stably expressing small interfering RNAs (siRNAs) specific for transcripts encoding the mu2, muNS, and sigmaNS proteins of strain type 3 Dearing (T3D). Infectivity assays revealed that yields of T3D, but not those of strain type 1 Lang, were significantly decreased in 293T cells stably expressing mu2, muNS, or sigmaNS siRNA. Stable expression of siRNAs specific for any one of these proteins substantially diminished viral dsRNA, protein synthesis, and inclusion formation, indicating that each is a critical component of the viral replication machinery. Using cell lines stably expressing muNS siRNA, we developed a complementation system to rescue viral replication by transient transfection with recombinant T3D muNS in which silent mutations were introduced into the sequence targeted by the muNS siRNA. Furthermore, we demonstrated that muNSC, which lacks the first 40 amino residues of muNS, is incapable of restoring reovirus growth in the complementation system. These results reveal interdependent functions for viral inclusion proteins and indicate that cell lines stably expressing reovirus siRNAs are useful tools for the study of viral protein structure-function relationships.
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Affiliation(s)
- Takeshi Kobayashi
- Department of Pediatrics, and Lamb Center for Pediatric Research (D7235 MCN), Vanderbilt University School of Medicine, Nashville, TN 37232, USA
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11
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Noad L, Shou J, Coombs KM, Duncan R. Sequences of avian reovirus M1, M2 and M3 genes and predicted structure/function of the encoded mu proteins. Virus Res 2006; 116:45-57. [PMID: 16297481 PMCID: PMC5123877 DOI: 10.1016/j.virusres.2005.08.014] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2005] [Revised: 08/23/2005] [Accepted: 08/24/2005] [Indexed: 12/29/2022]
Abstract
We report the first sequence analysis of the entire complement of M-class genome segments of an avian reovirus (ARV). We analyzed the M1, M2 and M3 genome segment sequences, and sequences of the corresponding muA, muB and muNS proteins, of two virus strains, ARV138 and ARV176. The ARV M1 genes were 2,283 nucleotides in length and predicted to encode muA proteins of 732 residues. Alignment of the homologous mammalian reovirus (MRV) mu2 and ARV muA proteins revealed a relatively low overall amino acid identity ( approximately 30%), although several highly conserved regions were identified that may contribute to conserved structural and/or functional properties of this minor core protein (i.e. the MRV mu2 protein is an NTPase and a putative RNA-dependent RNA polymerase cofactor). The ARV M2 genes were 2158 nucleotides in length, encoding predicted muB major outer capsid proteins of 676 amino acids, more than 30 amino acids shorter than the homologous MRV mu1 proteins. In spite of the difference in size, the ARV/MRV muB/mu1 proteins were more conserved than any of the homologous proteins encoded by other M- or S-class genome segments, exhibiting percent amino acid identities of approximately 45%. The conserved regions included the residues involved in the maturation- and entry- specific proteolytic cleavages that occur in the MRV mu1 protein. Notably missing was a region recently implicated in MRV mu1 stabilization and in forming "hub and spokes" complexes in the MRV outer capsid. The ARV M3 genes were 1996 nucleotides in length and predicted to encode a muNS non-structural protein of 635 amino acids, significantly shorter than the homologous MRV muNS protein, which is attributed to several substantial deletions in the aligned ARV muNS proteins. Alignments of the ARV and MRV muNS proteins revealed a low overall amino acid identity ( approximately 25%), although several regions were relatively conserved.
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Affiliation(s)
- Lindsay Noad
- Department of Medical Microbiology and Infectious Diseases, University of Manitoba, Winnipeg, Man., Canada R3E 0W3
| | - Jingyun Shou
- Department of Microbiology and Immunology, Dalhousie University, Halifax, NS, Canada B3H 4H7
| | - Kevin M. Coombs
- Department of Medical Microbiology and Infectious Diseases, University of Manitoba, Winnipeg, Man., Canada R3E 0W3
| | - Roy Duncan
- Department of Microbiology and Immunology, Dalhousie University, Halifax, NS, Canada B3H 4H7
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Broering TJ, Arnold MM, Miller CL, Hurt JA, Joyce PL, Nibert ML. Carboxyl-proximal regions of reovirus nonstructural protein muNS necessary and sufficient for forming factory-like inclusions. J Virol 2005; 79:6194-206. [PMID: 15858004 PMCID: PMC1091696 DOI: 10.1128/jvi.79.10.6194-6206.2005] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Mammalian orthoreoviruses are believed to replicate in distinctive, cytoplasmic inclusion bodies, commonly called viral factories or viroplasms. The viral nonstructural protein muNS has been implicated in forming the matrix of these structures, as well as in recruiting other components to them for putative roles in genome replication and particle assembly. In this study, we sought to identify the regions of muNS that are involved in forming factory-like inclusions in transfected cells in the absence of infection or other viral proteins. Sequences in the carboxyl-terminal one-third of the 721-residue muNS protein were linked to this activity. Deletion of as few as eight residues from the carboxyl terminus of muNS resulted in loss of inclusion formation, suggesting that some portion of these residues is required for the phenotype. A region spanning residues 471 to 721 of muNS was the smallest one shown to be sufficient for forming factory-like inclusions. The region from positions 471 to 721 (471-721 region) includes both of two previously predicted coiled-coil segments in muNS, suggesting that one or both of these segments may also be required for inclusion formation. Deletion of the more amino-terminal one of the two predicted coiled-coil segments from the 471-721 region resulted in loss of the phenotype, although replacement of this segment with Aequorea victoria green fluorescent protein, which is known to weakly dimerize, largely restored inclusion formation. Sequences between the two predicted coiled-coil segments were also required for forming factory-like inclusions, and mutation of either one His residue (His570) or one Cys residue (Cys572) within these sequences disrupted the phenotype. The His and Cys residues are part of a small consensus motif that is conserved across muNS homologs from avian orthoreoviruses and aquareoviruses, suggesting this motif may have a common function in these related viruses. The inclusion-forming 471-721 region of muNS was shown to provide a useful platform for the presentation of peptides for studies of protein-protein association through colocalization to factory-like inclusions in transfected cells.
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Affiliation(s)
- Teresa J Broering
- Department of Microbiology and Molecular Genetics, Harvard Medical School, 200 Longwood Ave., Boston, MA 02115, USA
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13
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Xu W, Patrick MK, Hazelton PR, Coombs KM. Avian reovirus temperature-sensitive mutant tsA12 has a lesion in major core protein sigmaA and is defective in assembly. J Virol 2004; 78:11142-51. [PMID: 15452234 PMCID: PMC521821 DOI: 10.1128/jvi.78.20.11142-11151.2004] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2004] [Accepted: 05/18/2004] [Indexed: 11/20/2022] Open
Abstract
Members of our laboratory previously generated and described a set of avian reovirus (ARV) temperature-sensitive (ts) mutants and assigned 11 of them to 7 of the 10 expected recombination groups, named A through G (M. Patrick, R. Duncan, and K. M. Coombs, Virology 284:113-122, 2001). This report presents a more detailed analysis of two of these mutants (tsA12 and tsA146), which were previously assigned to recombination group A. The capacities of tsA12 and tsA146 to replicate at a variety of temperatures were determined. Morphological analyses indicated that cells infected with tsA12 at a nonpermissive temperature produced approximately 100-fold fewer particles than cells infected at a permissive temperature and accumulated core particles. Cells infected with tsA146 at a nonpermissive temperature also produced approximately 100-fold fewer particles, a larger proportion of which were intact virions. We crossed tsA12 with ARV strain 176 to generate reassortant clones and used them to map the temperature-sensitive lesion in tsA12 to the S2 gene. S2 encodes the major core protein sigmaA. Sequence analysis of the tsA12 S2 gene showed a single alteration, a cytosine-to-uracil transition, at nucleotide position 488. This alteration leads to a predicted amino acid change from proline to leucine at amino acid position 158 in the sigmaA protein. An analysis of the core crystal structure of the closely related mammalian reovirus suggested that the Leu(158) substitution in ARV sigmaA lies directly under the outer face of the sigmaA protein. This may cause a perturbation in sigmaA such that outer capsid proteins are incapable of condensing onto nascent cores. Thus, the ARV tsA12 mutant represents a novel assembly-defective orthoreovirus clone that may prove useful for delineating virus assembly.
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Affiliation(s)
- Wanhong Xu
- Department of Medical Microbiology and Infectious Diseases, University of Manitoba, Winnipeg, Manitoba, Canada R3E 0W3
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14
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Broering TJ, Kim J, Miller CL, Piggott CDS, Dinoso JB, Nibert ML, Parker JSL. Reovirus nonstructural protein mu NS recruits viral core surface proteins and entering core particles to factory-like inclusions. J Virol 2004; 78:1882-92. [PMID: 14747553 PMCID: PMC369481 DOI: 10.1128/jvi.78.4.1882-1892.2004] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2003] [Accepted: 10/28/2003] [Indexed: 11/20/2022] Open
Abstract
Mammalian reoviruses are thought to assemble and replicate within cytoplasmic, nonmembranous structures called viral factories. The viral nonstructural protein mu NS forms factory-like globular inclusions when expressed in the absence of other viral proteins and binds to the surfaces of the viral core particles in vitro. Given these previous observations, we hypothesized that one or more of the core surface proteins may be recruited to viral factories through specific associations with mu NS. We found that all three of these proteins--lambda 1, lambda 2, and sigma 2--localized to factories in infected cells but were diffusely distributed through the cytoplasm and nucleus when each was separately expressed in the absence of other viral proteins. When separately coexpressed with mu NS, on the other hand, each core surface protein colocalized with mu NS in globular inclusions, supporting the initial hypothesis. We also found that lambda 1, lambda 2, and sigma 2 each localized to filamentous inclusions formed upon the coexpression of mu NS and mu 2, a structurally minor core protein that associates with microtubules. The first 40 residues of mu NS, which are required for association with mu 2 and the RNA-binding nonstructural protein sigma NS, were not required for association with any of the three core surface proteins. When coexpressed with mu 2 in the absence of mu NS, each of the core surface proteins was diffusely distributed and displayed only sporadic, weak associations with mu 2 on filaments. Many of the core particles that entered the cytoplasm of cycloheximide-treated cells following entry and partial uncoating were recruited to inclusions of mu NS that had been preformed in those cells, providing evidence that mu NS can bind to the surfaces of cores in vivo. These findings expand a model for how viral and cellular components are recruited to the viral factories in infected cells and provide further evidence for the central but distinct roles of viral proteins mu NS and mu 2 in this process.
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Affiliation(s)
- Teresa J Broering
- Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, Massachusetts 02115, USA
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15
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O'Donnell SM, Hansberger MW, Dermody TS. Viral and cellular determinants of apoptosis induced by mammalian reovirus. Int Rev Immunol 2003; 22:477-503. [PMID: 12959755 DOI: 10.1080/08830180305212] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Mammalian reoviruses serve as important models for studies of viral replication and pathogenesis. These viruses have been isolated from many mammalian species, including humans, and cause disease primarily in the very young. Reoviruses induce apoptosis by a novel mechanism that requires engagement of cell-surface receptors, intracellular signal transduction, and activation of NF-kappaB. Reovirus binding to both cell-surface sialic acid and junctional adhesion molecule 1 is required for NF-kappaB activation and apoptosis. However, receptor binding alone is not sufficient to evoke these events. Viral disassembly acts in concert with receptor binding to induce NF-kappaB activation and apoptosis. Nuclear translocation of NF-kappaB is followed by activation of both extrinsic and intrinsic cell-death pathways. Importantly, potently apoptotic reovirus strains are highly virulent in newborn mice, suggesting that NF-kappaB-dependent apoptosis is essential for reovirus-induced disease.
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Affiliation(s)
- Sean M O'Donnell
- Department of Pediatrics and Elizabeth B. Lamb Center for Pediatric Research, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
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16
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Becker MM, Peters TR, Dermody TS. Reovirus sigma NS and mu NS proteins form cytoplasmic inclusion structures in the absence of viral infection. J Virol 2003; 77:5948-63. [PMID: 12719587 PMCID: PMC154006 DOI: 10.1128/jvi.77.10.5948-5963.2003] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2002] [Accepted: 02/24/2003] [Indexed: 11/20/2022] Open
Abstract
Reovirus replication occurs in the cytoplasm of infected cells and culminates in the formation of crystalline arrays of progeny virions within viral inclusions. Two viral nonstructural proteins, sigma NS and micro NS, and structural protein sigma 3 form protein-RNA complexes early in reovirus infection. To better understand the minimal requirements of viral inclusion formation, we expressed sigma NS, mu NS, and sigma 3 alone and in combination in the absence of viral infection. In contrast to its concentration in inclusion structures during reovirus replication, sigma NS expressed in cells in the absence of infection is distributed diffusely throughout the cytoplasm and does not form structures that resemble viral inclusions. Expressed sigma NS is functional as it complements the defect in temperature-sensitive, sigma NS-mutant virus tsE320. In both transfected and infected cells, mu NS is found in punctate cytoplasmic structures and sigma 3 is distributed diffusely in the cytoplasm and the nucleus. The subcellular localization of mu NS and sigma 3 is not altered when the proteins are expressed together or with sigma NS. However, when expressed with micro NS, sigma NS colocalizes with mu NS to punctate structures similar in morphology to inclusion structures observed early in viral replication. During reovirus infection, both sigma NS and mu NS are detectable 4 h after adsorption and colocalize to punctate structures throughout the viral life cycle. In concordance with these results, sigma NS interacts with mu NS in a yeast two-hybrid assay and by coimmunoprecipitation analysis. These data suggest that sigma NS and mu NS are the minimal viral components required to form inclusions, which then recruit other reovirus proteins and RNA to initiate viral genome replication.
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Affiliation(s)
- Michelle M Becker
- Department of Microbiology and Immunology and Elizabeth B. Lamb Center for Pediatric Research, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA
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Kim J, Zhang X, Centonze VE, Bowman VD, Noble S, Baker TS, Nibert ML. The hydrophilic amino-terminal arm of reovirus core shell protein lambda1 is dispensable for particle assembly. J Virol 2002; 76:12211-22. [PMID: 12414960 PMCID: PMC136864 DOI: 10.1128/jvi.76.23.12211-12222.2002] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The reovirus core particle is a molecular machine that mediates synthesis, capping, and export of the viral plus strand RNA transcripts. Its assembly and structure-function relationships remain to be well understood. Following the lead of previous studies with other Reoviridae family members, most notably orbiviruses and rotaviruses, we used recombinant baculoviruses to coexpress reovirus core proteins lambda1, lambda2, and sigma2 in insect cells. The resulting core-like particles (CLPs) were purified and characterized. They were found to be similar to cores with regard to their sizes, morphologies, and protein compositions. Like cores, they could also be coated in vitro with the two major outer-capsid proteins, micro 1 and sigma3, to produce virion-like particles. Coexpression of core shell protein lambda1 and core nodule protein sigma2 was sufficient to yield CLPs that could withstand purification, whereas expression of lambda1 alone was not, indicating a required role for sigma2 as a previous study also suggested. In addition, CLPs that lacked lambda2 (formed from lambda1 and sigma2 only) could not be coated with micro 1 and sigma3, indicating a required role for lambda2 in the assembly of these outer-capsid proteins into particles. To extend the use of this system for understanding the core and its assembly, we addressed the hypothesis that the hydrophilic amino-terminal region of lambda1, which adopts an extended arm-like conformation around each threefold axis in the reovirus core crystal structure, plays an important role in assembling the core shell. Using a series of lambda1 deletion mutants, we showed that the amino-terminal 230 residues of lambda1, including its zinc finger, are dispensable for CLP assembly. Residues in the 231-to-259 region of lambda1, however, were required. The core crystal structure suggests that residues in the 231-to-259 region are necessary because they affect the interaction of lambda1 with the threefold and/or fivefold copies of sigma2. An effective system for studies of reovirus core structure, assembly, and functions is hereby established.
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Affiliation(s)
- Jonghwa Kim
- Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, Massachusetts 02115, USA
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18
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Broering TJ, Parker JSL, Joyce PL, Kim J, Nibert ML. Mammalian reovirus nonstructural protein microNS forms large inclusions and colocalizes with reovirus microtubule-associated protein micro2 in transfected cells. J Virol 2002; 76:8285-97. [PMID: 12134034 PMCID: PMC155143 DOI: 10.1128/jvi.76.16.8285-8297.2002] [Citation(s) in RCA: 109] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Cells infected with mammalian orthoreoviruses contain large cytoplasmic phase-dense inclusions believed to be the sites of viral replication and assembly, but the morphogenesis, structure, and specific functions of these "viral factories" are poorly understood. Using immunofluorescence microscopy, we found that reovirus nonstructural protein microNS expressed in transfected cells forms inclusions that resemble the globular viral factories formed in cells infected with reovirus strain type 3 Dearing from our laboratory (T3D(N)). In the transfected cells, the formation of microNS large globular perinuclear inclusions was dependent on the microtubule network, as demonstrated by the appearance of many smaller microNS globular inclusions dispersed throughout the cytoplasm after treatment with the microtubule-depolymerizing drug nocodazole. Coexpression of microNS and reovirus protein micro2 from a different strain, type 1 Lang (T1L), which forms filamentous viral factories, altered the distributions of both proteins. In cotransfected cells, the two proteins colocalized in thick filamentous structures. After nocodazole treatment, many small dispersed globular inclusions containing microNS and micro2 were seen, demonstrating that the microtubule network is required for the formation of the filamentous structures. When coexpressed, the micro2 protein from T3D(N) also colocalized with microNS, but in globular inclusions rather than filamentous structures. The morphology difference between the globular inclusions containing microNS and micro2 protein from T3D(N) and the filamentous structures containing microNS and micro2 protein from T1L in cotransfected cells mimicked the morphology difference between globular and filamentous factories in reovirus-infected cells, which is determined by the micro2-encoding M1 genome segment. We found that the first 40 amino acids of microNS are required for colocalization with micro2 but not for inclusion formation. Similarly, a fusion of microNS amino acids 1 to 41 to green fluorescent protein was sufficient for colocalization with the micro2 protein from T1L but not for inclusion formation. These observations suggest a functional difference between microNS and microNSC, a smaller form of the protein that is present in infected cells and that is missing amino acids from the amino terminus of microNS. The capacity of microNS to form inclusions and to colocalize with micro2 in transfected cells suggests a key role for microNS in forming viral factories in reovirus-infected cells.
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Affiliation(s)
- Teresa J Broering
- Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, Massachusetts 02115, USA
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Becker MM, Goral MI, Hazelton PR, Baer GS, Rodgers SE, Brown EG, Coombs KM, Dermody TS. Reovirus sigmaNS protein is required for nucleation of viral assembly complexes and formation of viral inclusions. J Virol 2001; 75:1459-75. [PMID: 11152519 PMCID: PMC114052 DOI: 10.1128/jvi.75.3.1459-1475.2001] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2000] [Accepted: 10/26/2000] [Indexed: 11/20/2022] Open
Abstract
Progeny virions of mammalian reoviruses are assembled in the cytoplasm of infected cells at discrete sites termed viral inclusions. Studies of temperature-sensitive (ts) mutant viruses indicate that nonstructural protein sigmaNS and core protein mu2 are required for synthesis of double-stranded (ds) RNA, a process that occurs at sites of viral assembly. We used confocal immunofluorescence microscopy and ts mutant reoviruses to define the roles of sigmaNS and mu2 in viral inclusion formation. In cells infected with wild-type (wt) reovirus, sigmaNS and mu2 colocalize to large, perinuclear structures that correspond to viral inclusions. In cells infected at a nonpermissive temperature with sigmaNS-mutant virus tsE320, sigmaNS is distributed diffusely in the cytoplasm and mu2 is contained in small, punctate foci that do not resemble viral inclusions. In cells infected at a nonpermissive temperature with mu2-mutant virus tsH11.2, mu2 is distributed diffusely in the cytoplasm and the nucleus. However, sigmaNS localizes to discrete structures in the cytoplasm that contain other viral proteins and are morphologically indistinguishable from viral inclusions seen in cells infected with wt reovirus. Examination of cells infected with wt reovirus over a time course demonstrates that sigmaNS precedes mu2 in localization to viral inclusions. These findings suggest that viral RNA-protein complexes containing sigmaNS nucleate sites of viral replication to which other viral proteins, including mu2, are recruited to commence dsRNA synthesis.
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Affiliation(s)
- M M Becker
- Departments of Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA
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20
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Farsetta DL, Chandran K, Nibert ML. Transcriptional activities of reovirus RNA polymerase in recoated cores. Initiation and elongation are regulated by separate mechanisms. J Biol Chem 2000; 275:39693-701. [PMID: 11007773 DOI: 10.1074/jbc.m004562200] [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: 11/06/2022] Open
Abstract
The particle-associated reovirus polymerase synthesizes mRNA within only certain viral particle types. Reovirus cores, subviral particles lacking outer capsid proteins mu1, sigma3, and sigma1, produce mRNA and abortive transcripts. Reovirus virions, which contain complete outer capsids, cannot produce mRNA and produce few abortive transcripts. Recoated cores are virion-like particles generated by the addition of recombinant outer capsid proteins to cores. We used recoated cores to analyze transcriptional regulation by reovirus outer capsid proteins. Partially recoated particles, containing less than virion amounts of mu1 and sigma3, synthesized mRNA at levels inversely proportional to outer capsid protein levels. Fully recoated cores exhibited undetectable mRNA synthesis levels, as did virions. However, recoated cores produced high levels of abortive transcripts. Recoated core abortive transcripts remained particle-associated and appeared to inhibit further abortive transcript production. Proteolysis of recoated cores removing mu1 and sigma3 released accumulated abortive transcripts and relieved inhibition of mRNA and abortive transcript synthesis. These results suggest transcriptional elongation, but not initiation, is blocked by virion-like amounts of mu1 and sigma3. Particle-associated abortive transcripts may down-regulate transcriptional initiation. Minor outer capsid protein sigma1 had no demonstrable effect on transcriptional activities. Transcriptional regulation may ensure progeny virions do not compete with transcribing particles for ribonucleoside triphosphates.
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Affiliation(s)
- D L Farsetta
- Department of Biochemistry, Institute for Molecular Virology, and Cell and Molecular Biology Program, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
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21
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Patton JT, Spencer E. Genome replication and packaging of segmented double-stranded RNA viruses. Virology 2000; 277:217-25. [PMID: 11080470 DOI: 10.1006/viro.2000.0645] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Affiliation(s)
- J T Patton
- Laboratory of Infectious Diseases, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, 7 Center Drive, MSC 0720, Room 117, Bethesda, Maryland 20892, USA.
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22
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Broering TJ, McCutcheon AM, Centonze VE, Nibert ML. Reovirus nonstructural protein muNS binds to core particles but does not inhibit their transcription and capping activities. J Virol 2000; 74:5516-24. [PMID: 10823857 PMCID: PMC112037 DOI: 10.1128/jvi.74.12.5516-5524.2000] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Previous studies provided evidence that nonstructural protein muNS of mammalian reoviruses is present in particle assembly intermediates isolated from infected cells. Morgan and Zweerink (Virology 68:455-466, 1975) showed that a subset of these intermediates, which can synthesize the viral plus strand RNA transcripts in vitro, comprise core-like particles plus large amounts of muNS. Given the possible role of muNS in particle assembly and/or transcription implied by those findings, we tested whether recombinant muNS can bind to cores in vitro. The muNS protein bound to cores, but not to two particle forms, virions and intermediate subvirion particles, that contain additional outer-capsid proteins. Incubating cores with increasing amounts of muNS resulted in particle complexes of progressively decreasing buoyant density, approaching the density of protein alone when very large amounts of muNS were bound. Thus, the muNS-core interaction did not exhibit saturation or a defined stoichiometry. Negative-stain electron microscopy of the muNS-bound cores revealed that the cores were intact and linked together in large complexes by an amorphous density, which we ascribe to muNS. The muNS-core complexes retained the capacity to synthesize the viral plus strand transcripts as well as the capacity to add methylated caps to the 5' ends of the transcripts. In vitro competition assays showed that mixing muNS with cores greatly reduced the formation of recoated cores by stoichiometric binding of outer-capsid proteins mu1 and sigma3. These findings are consistent with the presence of muNS in transcriptase particles as described previously and suggest that, by binding to cores in the infected cell, muNS may block or delay outer-capsid assembly and allow continued transcription by these particles.
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Affiliation(s)
- T J Broering
- Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
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23
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McCutcheon AM, Broering TJ, Nibert ML. Mammalian reovirus M3 gene sequences and conservation of coiled-coil motifs near the carboxyl terminus of the microNS protein. Virology 1999; 264:16-24. [PMID: 10544126 DOI: 10.1006/viro.1999.9990] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Nucleotide sequences of the mammalian orthoreovirus (reovirus) type 1 Lang and type 2 Jones M3 gene segments were newly determined. The nucleotide sequence of the reovirus type 3 Dearing M3 segment also was determined to compare with a previously reported M3 sequence for that isolate. Comparisons showed Lang and Dearing M3 to be more closely related than either was to Jones M3, consistent with previous findings for other reovirus gene segments. The microNS protein sequences deduced from each M3 segment were shown to be related in a similar pattern as the respective nucleotide sequences and to contain several regions of greater or less than average variability among the three isolates. Identification of conserved methionine codons near the 5' ends of the Lang, Jones, and Dearing M3 plus strands lent support to the hypothesis that microNSC, a smaller protein also encoded by M3, arises by translation initiation from a downstream methionine codon within the same open reading frame as microNS. Other analyses of the deduced protein sequences indicated that regions within the carboxyl-terminal third of microNS and microNSC from each isolate have a propensity to form alpha-helical coiled coils, most likely coiled-coil dimers. The new sequences will augment further studies on microNS and microNSC structure and function.
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Affiliation(s)
- A M McCutcheon
- The College of Agricultural and Life Sciences, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
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24
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Hazelton PR, Coombs KM. The reovirus mutant tsA279 L2 gene is associated with generation of a spikeless core particle: implications for capsid assembly. J Virol 1999; 73:2298-308. [PMID: 9971813 PMCID: PMC104475 DOI: 10.1128/jvi.73.3.2298-2308.1999] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/1998] [Accepted: 11/23/1998] [Indexed: 11/20/2022] Open
Abstract
Previous studies which used intertypic reassortants of the wild-type reovirus serotype 1 Lang and the temperature-sensitive (ts) serotype 3 mutant clone tsA279 identified two ts lesions; one lesion, in the M2 gene segment, was associated with defective transmembrane transport of restrictively assembled virions (P. R. Hazelton and K. M. Coombs, Virology 207:46-58, 1995). In the present study we show that the second lesion, in the L2 gene segment, which encodes the lambda2 protein, is associated with the accumulation of a core-like particle defective for the lambda2 pentameric spike. Physicochemical, biochemical, and immunological studies showed that these structures were deficient for genomic double-stranded RNA, the core spike protein lambda2, and the minor core protein micro2. Core particles with the lambda2 spike structure accumulated after temperature shift-down from a restrictive to a permissive temperature in the presence of cycloheximide. These data suggest the spike-deficient, core-like particle is an assembly intermediate in reovirus morphogenesis. The existence of this naturally occurring primary core structure suggests that the core proteins lambda1, lambda3, and sigma2 interact to initiate the process of virion capsid assembly through a dodecahedral mechanism. The next step in the proposed capsid assembly model would be the association of the minor core protein mu2, either preceding or collateral to the condensation of the lambda2 pentameric spike at the apices of the primary core structure. The assembly pathway of the reovirus double capsid is further elaborated when these observations are combined with structures identified in other studies.
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Affiliation(s)
- P R Hazelton
- Department of Medical Microbiology and Infectious Diseases, University of Manitoba, Winnipeg, Manitoba, Canada R3E 0W3
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25
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Schiff LA. Reovirus capsid proteins sigma 3 and mu 1: interactions that influence viral entry, assembly, and translational control. Curr Top Microbiol Immunol 1998; 233:167-83. [PMID: 9599926 DOI: 10.1007/978-3-642-72092-5_8] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- L A Schiff
- Department of Microbiology, University of Minnesota, Minneapolis 55455, USA
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26
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Affiliation(s)
- M L Nibert
- Institute for Molecular Virology, Graduate School, University of Wisconsin-Madison 53706, USA
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27
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Joklik WK, Roner MR. Molecular recognition in the assembly of the segmented reovirus genome. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 1996; 53:249-81. [PMID: 8650305 DOI: 10.1016/s0079-6603(08)60147-6] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Affiliation(s)
- W K Joklik
- Department of Microbiology, Duke University Medical Center, Durham, North Carolina 27710, USA
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28
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Affiliation(s)
- W K Joklik
- Department of Microbiology, Duke University Medical Center, Durham, North Carolina 27710
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29
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Antczak JB, Joklik WK. Reovirus genome segment assortment into progeny genomes studied by the use of monoclonal antibodies directed against reovirus proteins. Virology 1992; 187:760-76. [PMID: 1546466 DOI: 10.1016/0042-6822(92)90478-8] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Using a panel of monoclonal antibodies (MABs) against reovirus proteins, we have identified proteins that associate with reovirus messenger RNA molecules prior to the generation of progeny double-stranded (ds) genome segments and proteins that are components of the structures within which progeny ds genome segments are generated. The following conclusions can be drawn from the results obtained. (1) Three proteins rapidly become associated with mRNA molecules to form single-stranded RNA-containing complexes (ssRCCs): the nonstructural protein microNS, the nonstructural protein sigma NS, and protein sigma 3. (2) Analysis of populations of ssRCCs in density gradients and by sequential exposure to various MABs indicates that some ssRCCs contain only microNS, others microNS and sigma NS or sigma 3, and others all three proteins. Each ssRCC contains one RNA molecule and, depending on the size of the RNA, 10-30 protein molecules. (3) The relative proportions of the individual RNA species in the ssRCC populations reflect the composition of the total mRNA population present in infected cells (which differs substantially from equimolarity). (4) RCCs that contain dsRNA, which become detectable as early as 4 hr after infection, contain not only microNS, sigma NS, and sigma 3, but also lambda 2. (5) The relative proportions of the 10 genome segments in dsRCCs are equimolar. This suggests that genome segment assortment into progeny genomes is linked to the transcription of plus strands into minus strands.
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Affiliation(s)
- J B Antczak
- Department of Microbiology and Immunology, Duke University Medical Center, Durham, North Carolina 27710
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30
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Affiliation(s)
- A R Bellamy
- Department of Cellular and Molecular Biology, University of Auckland, New Zealand
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31
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Affiliation(s)
- B T Eaton
- Australian Animal Health Laboratory, C.S.I.R.O., Geelong Victoria, Australia
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Abstract
To understand the role of viral proteins in the replication of rotavirus RNA, we have characterized the structure of subviral particles (SVPs) that synthesize double-stranded RNA (DS RNA). Pulse-labeling of newly made RNA in infected cells showed that rotavirus DS RNA was synthesized either in single-shell (SS)-like particles or in precursor particles that rapidly mature into SS particles. Experiments using a cell-free system demonstrated that most replicase particles containing newly made DS RNA were of greater density in CsCl than single-shelled (SS) particles. However, this was partly due to the presence of single-stranded RNAs as the treatment of replicase particles with micrococcal nuclease reduced their density to between core particles and SS particles. Electrophoretic analysis indicated that replicase particles, purified by centrifugation on CsCl and glycerol gradients, were similar to SS particles, containing the structural proteins VP1, VP2, and VP6. Rotavirus replicase particles were also found to contain the nonstructural proteins NS34 and NS35 and possible host components. The presence of VP6 in enzymatically active replicase particles suggests that, like transcription, this protein may be required for rotavirus RNA replication.
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Affiliation(s)
- J T Patton
- Department of Microbiology and Immunology, University of Miami School of Medicine, Florida 33101
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33
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Mora M, Partin K, Bhatia M, Partin J, Carter C. Association of reovirus proteins with the structural matrix of infected cells. Virology 1987; 159:265-77. [PMID: 3617500 DOI: 10.1016/0042-6822(87)90464-8] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The interaction of reovirus with the cytoskeleton was investigated. The soluble components of infected cells were extracted with the nonionic detergent NP-40 in a physiological buffer, and a cytoskeletal extract was prepared from the detergent-insoluble fraction. We observed a selective association of viral-specified products with the cytoskeleton that was temporally controlled. Viral dsRNA appeared first on the framework but after several hours was found also in the soluble phase, encapsidated in mature virions. The initial viral translation products were associated exclusively with the soluble fraction, but concomitant with the appearance of dsRNA, viral proteins microNS and sigma 3 were detected on the cytoskeleton. Several hours later, all viral proteins were detected on the framework. Viral polypeptide microNS exhibited unique spatial distribution patterns that correlated with viral assembly: Before dsRNA replication, it appeared as diffusely distributed protein; a few hours later, it was detected in punctate foci interconnected by tiny filaments; several hours later, it appeared as an extensive fiber network that traversed the foci. The other viral proteins were detected only within viral foci. MicroNS remained bound to the matrix fraction after treatment with DNase, Mg2+, and high salt, treatments that released other viral proteins. This distribution pattern was virus-directed because passage of virus at high multiplicity of infection induced mutations that prevented assembly of the microNS-coated filament organization. A small fraction of the viral-specified products that included polypeptide microNS, but not viral dsRNA, was coprecipitated from cytoskeletal extracts with proteins of mol wt approximately 55K by monoclonal antibodies that recognized tubulin and vimentin. Disruption of this interaction by long exposure to colchicine did not prevent association of viral proteins or RNA with the matrix, indicating that viral products were not transported through these interactions. The results indicate that reovirus morphogenesis includes temporal and spatial controls not described previously.
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34
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Samuel CE, Duncan R, Knutson GS, Hershey JW. Mechanism of interferon action. Increased phosphorylation of protein synthesis initiation factor eIF-2 alpha in interferon-treated, reovirus-infected mouse L929 fibroblasts in vitro and in vivo. J Biol Chem 1984. [DOI: 10.1016/s0021-9258(18)90715-5] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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35
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36
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Walden W, Godefroy-Colburn T, Thach R. The role of mRNA competition in regulating translation. I. Demonstration of competition in vivo. J Biol Chem 1981. [DOI: 10.1016/s0021-9258(19)68468-1] [Citation(s) in RCA: 60] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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37
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Lee PW, Hayes EC, Joklik WK. Characterization of anti-reovirus immunoglobulins secreted by cloned hybridoma cell lines. Virology 1981; 108:134-46. [PMID: 7269233 DOI: 10.1016/0042-6822(81)90533-x] [Citation(s) in RCA: 128] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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38
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39
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Abstract
The involvement of light (L) and dense (D) bovine rotavirus particle types during virus replication has been studied. It was found that infectious parental L virions are uncoated in vivo to a particle similar to native D particles. Differences in the rate of synthesis and relative yields of L and D particles in MDBK and MA-104 cells have been detected. Results from pulse-chase labeling experiments indicate that D particles serve as morphogenic precursors to the complete L virion.
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40
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41
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42
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43
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Gomatos PJ, Kuechenthal I. Reovirus-specific enzyme(s) associated with subviral particles responds in vitro to polyribocytidylate to yield double-stranded polyribocytidylate-polyriboguanylate. J Virol 1977; 23:80-90. [PMID: 886647 PMCID: PMC515802 DOI: 10.1128/jvi.23.1.80-90.1977] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
In reovirus-infected cells, virus-specific particles accumulate that have associated with them a polyribocytidylate [poly(C)]-dependent polymerase. This enzyme copies in vitro poly(C) to yield the double-stranded poly(C).polyriboguanylate [poly(G)]. The particles with poly(C)-dependent polymerase were heterogeneous in size, with most sedimenting from 300S to 550S. Exponential increase in these particles began at 23 h, and maximal amounts were present by 31 h, the time of onset of exponential growth of virus at 30 degrees C. Maximal amounts of particles with active transcriptase and replicase were present at 15 and 18 h after infection. Thereafter, there was a marked decrease in particles with active transcriptase and replicase until base line levels were reached at 31 h. Thus, the increase in poly(C)-responding particles occurred coincident with the decrease in particles with active transcriptase and replicase. The requirement for poly(C) as template was specific because no RNA was synthesized in vitro in response to any other homopolymer, including 2'-O-methyl-poly(C). Synthesis was optimal in the presence of Mn(2+) as the divalent cation, and no primer was necessary for synthesis. In contrast, the dinucleotide GpG markedly stimulated synthesis in the presence of 8 mM Mg(2+). The size of the poly(C).poly(G) synthesized in vitro was dependent on the size of the poly(C) used as template. This suggested that the whole template was copied into a complementary strand of similar size. The T(m) of the product was between 100 and 130 degrees C. Hydrolysis of the product labeled in [(32)P]GMP with alkali or RNase T2 yielded GMP as the only labeled mononucleotide. This does indicate that the synthesis of the poly(G) strand in vitro did not proceed by end addition to the poly(C) template, but proceeded on a separate strand.
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44
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Morgan EM, Zweerink HJ. Characterization of the double-stranded RNA in replicase particles in reovirus-infected cells. Virology 1977; 77:421-3. [PMID: 841868 DOI: 10.1016/0042-6822(77)90440-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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45
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Mindich L, Sinclair JF, Cohen J. The morphogenesis of bacteriophage phi6: particles formed by nonsense mutants. Virology 1976; 75:224-31. [PMID: 982850 DOI: 10.1016/0042-6822(76)90021-0] [Citation(s) in RCA: 64] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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46
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Zweerink HJ, Morgan EM, Skyler JS. Reovirus morphogenesis: characterization of subviral particles in infected cells. Virology 1976; 73:442-53. [PMID: 960572 DOI: 10.1016/0042-6822(76)90405-0] [Citation(s) in RCA: 33] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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47
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White CK, Zweerink HJ. Studies on the structure of reovirus cores: selective removal of polypeptide lambda 2. Virology 1976; 70:171-80. [PMID: 3879 DOI: 10.1016/0042-6822(76)90247-6] [Citation(s) in RCA: 63] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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