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Paul Ahlquist - One of the best experts on this subject based on the ideXlab platform.
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Parallels among positive-strand RNA Viruses, reverse-transcribing Viruses and Double-Stranded RNA Viruses
Nature Reviews Microbiology, 2006Co-Authors: Paul AhlquistAbstract:Despite major differences in the life cycles of the seven different classes of known Viruses, the genome-replication processes of certain positive-strand RNA Viruses, Double-Stranded RNA Viruses and reverse-transcribing Viruses show striking parallels. Paul Ahlquist highlights these similarities and discusses their intriguing evolutionary implications. Viruses are divided into seven classes on the basis of differing strategies for storing and replicating their genomes through RNA and/or DNA intermediates. Despite major differences among these classes, recent results reveal that the non-virion, intracellular RNA-replication complexes of some positive-strand RNA Viruses share parallels with the structure, assembly and function of the replicative cores of extracellular virions of reverse-transcribing Viruses and Double-Stranded RNA Viruses. Therefore, at least four of seven principal virus classes share several underlying features in genome replication and might have emerged from common ancestors. This has implications for virus function, evolution and control. Viruses are exceptionally diverse and are grouped by genome replication and encapsidation strategies into seven distinct classes: two classes of DNA Viruses (encapsidating single-stranded (ss)DNA or Double-Stranded (ds)DNA), three classes of RNA Viruses (encapsidating mRNA-sense ssRNA, antisense ssRNA or dsRNA) and two classes of reverse-transcribing Viruses (encapsidating RNA or DNA). Despite substantial life-cycle differences, positive-strand RNA ((+)RNA) Viruses, dsRNA Viruses and reverse-transcribing Viruses share multiple similarities in genome replication. All replicate their genomes through RNA intermediates that also serve as mRNAs. Moreover, the intracellular RNA-replication complexes of (+)RNA Viruses share similarities in structure, assembly and function with the polymerase-containing virion cores of dsRNA and reverse transcribing Viruses. Brome mosaic virus (BMV) RNA-replication factors 1a and 2a^pol and cis -acting template-recruitment signals parallel retrovirus Gag, Pol and RNA-packaging signals in virion assembly: 1a localizes to specific membranes, self-interacts and induces ∼60-nm membrane invaginations to which it recruits 2a^pol and viral RNAs for replication. Therefore, like retroViruses and dsRNA Viruses, BMV sequesters its genomic RNA and polymerase in a virus-induced compartment for replication. BMV and some other alphavirus-like (+)RNA Viruses also parallel retroViruses in using tRNA-related sequences to initiate genome replication, and share with dsRNA reoViruses aspects of the function and interaction of their RNA polymerase and RNA-capping enzymes. Emerging results indicate that the genome-replication machineries of these Viruses might share other mechanistic features. Whereas (+)RNA alphavirus-like Viruses, dsRNA reoViruses and retroViruses are linked by the above similarities, (+)RNA picoRNAViruses, dsRNA biRNAViruses and reverse-transcribing hepadnaViruses share some distinct features, including protein-primed nucleic-acid synthesis. Such parallels suggest that at least some (+)RNA Viruses, dsRNA Viruses and reverse-transcribing Viruses might have evolved from common ancestors. The transitions required for such evolution can be readily envisioned and some have precedents. These underlying parallels in genome replication by four of the seven main virus classes might provide a basis for more generalizable or broader-spectrum approaches for virus control.
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Parallels among positive-strand RNA Viruses, reverse-transcribing Viruses and Double-Stranded RNA Viruses
Nature Reviews Microbiology, 2006Co-Authors: Paul AhlquistAbstract:Viruses are divided into seven classes on the basis of differing strategies for storing and replicating their genomes through RNA and/or DNA intermediates. Despite major differences among these classes, recent results reveal that the non-virion, intracellular RNA-replication complexes of some positive-strand RNA Viruses share parallels with the structure, assembly and function of the replicative cores of extracellular virions of reverse-transcribing Viruses and Double-Stranded RNA Viruses. Therefore, at least four of seven principal virus classes share several underlying features in genome replication and might have emerged from common ancestors. This has implications for virus function, evolution and control. Despite major differences in the life cycles of the seven different classes of known Viruses, the genome-replication processes of certain positive-strand RNA Viruses, Double-Stranded RNA Viruses and reverse-transcribing Viruses show striking parallels. Paul Ahlquist highlights these similarities and discusses their intriguing evolutionary implications. Viruses are exceptionally diverse and are grouped by genome replication and encapsidation strategies into seven distinct classes: two classes of DNA Viruses (encapsidating single-stranded (ss)DNA or Double-Stranded (ds)DNA), three classes of RNA Viruses (encapsidating mRNA-sense ssRNA, antisense ssRNA or dsRNA) and two classes of reverse-transcribing Viruses (encapsidating RNA or DNA). Despite substantial life-cycle differences, positive-strand RNA ((+)RNA) Viruses, dsRNA Viruses and reverse-transcribing Viruses share multiple similarities in genome replication. All replicate their genomes through RNA intermediates that also serve as mRNAs. Moreover, the intracellular RNA-replication complexes of (+)RNA Viruses share similarities in structure, assembly and function with the polymerase-containing virion cores of dsRNA and reverse transcribing Viruses. Brome mosaic virus (BMV) RNA-replication factors 1a and 2a^pol and cis -acting template-recruitment signals parallel retrovirus Gag, Pol and RNA-packaging signals in virion assembly: 1a localizes to specific membranes, self-interacts and induces ∼60-nm membrane invaginations to which it recruits 2a^pol and viral RNAs for replication. Therefore, like retroViruses and dsRNA Viruses, BMV sequesters its genomic RNA and polymerase in a virus-induced compartment for replication. BMV and some other alphavirus-like (+)RNA Viruses also parallel retroViruses in using tRNA-related sequences to initiate genome replication, and share with dsRNA reoViruses aspects of the function and interaction of their RNA polymerase and RNA-capping enzymes. Emerging results indicate that the genome-replication machineries of these Viruses might share other mechanistic features. Whereas (+)RNA alphavirus-like Viruses, dsRNA reoViruses and retroViruses are linked by the above similarities, (+)RNA picoRNAViruses, dsRNA biRNAViruses and reverse-transcribing hepadnaViruses share some distinct features, including protein-primed nucleic-acid synthesis. Such parallels suggest that at least some (+)RNA Viruses, dsRNA Viruses and reverse-transcribing Viruses might have evolved from common ancestors. The transitions required for such evolution can be readily envisioned and some have precedents. These underlying parallels in genome replication by four of the seven main virus classes might provide a basis for more generalizable or broader-spectrum approaches for virus control.
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Parallels among positive-strand RNA Viruses, reverse-transcribing Viruses and Double-Stranded RNA Viruses.
Nature reviews. Microbiology, 2006Co-Authors: Paul AhlquistAbstract:Viruses are divided into seven classes on the basis of differing strategies for storing and replicating their genomes through RNA and/or DNA intermediates. Despite major differences among these classes, recent results reveal that the non-virion, intracellular RNA-replication complexes of some positive-strand RNA Viruses share parallels with the structure, assembly and function of the replicative cores of extracellular virions of reverse-transcribing Viruses and Double-Stranded RNA Viruses. Therefore, at least four of seven principal virus classes share several underlying features in genome replication and might have emerged from common ancestors. This has implications for virus function, evolution and control.
Reed B. Wickner - One of the best experts on this subject based on the ideXlab platform.
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Double-Stranded RNA Viruses of Saccharomyces cerevisiae.
Microbiological reviews, 1996Co-Authors: Reed B. WicknerAbstract:INFECTIOUS ELEMENTS OF SACCHAROMYCES CEREVISIAE 250 BIOLOGY OF THE YEAST dsRNA Viruses AND THE KILLER PHENOMENON 250 L-A VIRUS STRUCTURE: T 5 1 WITH 60 ASYMMETRIC Gag DIMERS 251 VIRAL REPLICATION CYCLES 251 L-A ENCODES Gag AND Gag-Pol 252 REPLICATION AND TRANSCRIPTION OF VIRAL RNA: IN VITRO SYSTEMS 254 TRANSLATION OF VIRAL mRNA 254 The SKI2,3,8 System Blocks the Translation of Non-Poly(A) mRNA 255 M1 Propagation Depends Critically on Free 60S Ribosomal Subunit Levels 256 Do SKI2, 3, and 8 Determine 60S Subunit Interaction with Poly(A)? 257 Gag Makes Decapitated Decoys To Distract the SKI1/XRN1 Exoribonuclease 257 Lethality of ski1 ski2 and ski1 ski3 double mutants 258 Gag-Pol Fusion Protein Formed by a 21 Ribosomal Frameshift: How and Why 258 Mechanism of 21 ribosomal frameshifting 258 How critical is the efficiency of frameshifting? 259 Chromosomal genes affecting the efficiency of frameshifting 259 Can 21 ribosomal frameshifting be used as a target of antiviral drugs? 259 POSTTRANSLATIONAL PROCESSING 259 MAK3 N-Acetyltransferase Modification of Gag Is Necessary for Assembly 259 Killer Preprotoxin Is Processed To Form Mature Toxin 260 KEX1 and KEX2 Processing Proteases and Mammalian Prohormone Processing 260 RNA PACKAGING: IN VITRO AND IN VIVO 260 Evidence for cis Packaging by L-A 260 Does Packaging Control Translation? 260 L-BC IS CLOSELY RELATED TO L-A 261 CONCLUSIONS AND PROSPECTS 261 REFERENCES 262
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fungal virus capsids cytoplasmic compartments for the replication of double stranded RNA formed as icosahedral shells of asymmetric gag dimers
Journal of Molecular Biology, 1994Co-Authors: Holland R Cheng, José R Castón, Benes L. Trus, Guo Ji Wang, Fei Gu, Thomas J Smith, Timothy S Baker, Robert F Bozarth, Naiqian Cheng, Reed B. WicknerAbstract:Abstract The primary functions of most virus capsids are to protect the viral genome in the extra-cellular milieu and deliver it to the host. In contrast, the capsids of fungal Viruses, like the cores of all other known double stranded RNA Viruses, are not involved in host recognition but do shield their genomes, and they also carry out transcription and replication. Nascent (+) strands are extruded from transcribing virions. The capsids of the yeast virus L-A are composed of Gag (capsid protein; 76 kDa), with a few molecules of Gag-Pol (170 kDa). Analysis of these 420 A diameter shells and those of the fungal P4 virus by cryo-electron microscopy and image reconstruction shows that they share the same novel icosahedral structure. Both capsids consist of 60 equivalent Gag dimers. whose two subunits occupy non-equivalent bonding environments. Stoichiometry data on other Double-Stranded RNA Viruses indicate that the 120-subunit structure is widespread, implying that this molecular architecture has features that are particularly favorable to the design of a capsid that is also a biosynthetic compartment.
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Assembly of Double-Stranded RNA Viruses: bacteriophage ø6 and yeast virus L-A
Seminars in Virology, 1994Co-Authors: Dennis H. Bamford, Reed B. WicknerAbstract:Abstract Double-Stranded RNA Viruses have a virion-associated RNA-dependent RNA polymerase activity which is involved in such critical steps of viral assembly as genome packaging and minus strand synthesis. In vitro studies of a bacterial dsRNA virus, o6, and a yeast virus, L-A, have shed light on capsid formation as well as on the protein/RNA interactions and packaging of the viral genomes. In the o6 system, an empty dodecahedral polymerase complex (procapsid) composed of four protein species is formed without the help of other viral proteins or RNA. This particle packages positive sense viral RNA genome segments in an ATP dependent reaction. The presence of all rNTPs allows the synthesis of complementary (-) strands within the particle. Self-assembly of an additional protein shell (composed of protein P8) around this particle takes place in the presence of Ca2+ ions. In vivo, these nucleocapsids obtain an envelope while still residing in the cell cytoplasm. L-A, in contrast, is not known to make a prohead structure. The Pol domain of L-A's Gag-Pol fusion protein is necessary for packaging of the (+) strand RNA and probably actually binds to the (+) strand packaging site (a stem-loop with a protruding A) insuring its packaging while the Gag domain primes polymerization of the coat protein. N-Acetylation of Gag by the host MAK3 N-acetyltransferase is necessary for proper assembly, and the ratio of Gag-Pol/Gag, determined by the efficiency of - 1 ribosomal frameshifting, is critical for propagation of the M1 satellite dsRNA.
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pol of gag pol fusion protein required for encapsidation of viral RNA of yeast l a virus
Nature, 1992Co-Authors: Tsutomu Fujimura, Juan Carlos Ribas, Alexandr M Makhov, Reed B. WicknerAbstract:Double-Stranded RNA Viruses have an RNA-dependent RNA polymerase activity associated with the viral particles which is indispensable for their replication cycle. Using the yeast L-A Double-Stranded RNA virus we have investigated the mechanism by which the virus encapsidates its genomic RNA and RNA polymerase. The L-A gag gene encodes the principal viral coat protein and the overlapping pol gene is expressed as a gag–pol fusion protein which is formed by a −1 ribosomal frameshift1–3. Here we show that Gag alone is sufficient for virus particle formation, but that it fails to package the viral single-stranded RNA genome. Encapsidation of the viral RNA requires only a part of the Pol region (the N-terminal quarter), which is presumably distinct from the RNA polymerase domain. Given that the Pol region has single-stranded RNA-binding activity, these results are consistent with our L-A virus encapsidation model1: the Pol region of the fusion protein binds specifically to the viral genome (+) strand, and the N-terminal gag-encoded region primes polymerization of Gag to form the capsid, thus ensuring the packaging of both the viral genome and the RNA polymerase.
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a 1 ribosomal frameshift in a double stranded RNA virus of yeast forms a gag pol fusion protein
Proceedings of the National Academy of Sciences of the United States of America, 1991Co-Authors: Jonathan D Dinman, Tateo Icho, Reed B. WicknerAbstract:Abstract The L-A Double-Stranded RNA (dsRNA) virus of Saccharomyces cerevisiae has two open reading frames (ORFs). ORF1 encodes the 80-kDa major coat protein (gag). ORF2, which is expressed only as a 180-kDa fusion protein with ORF1, encodes a single-stranded RNA-binding domain and has the consensus sequence for RNA-dependent RNA polymerases of (+)-strand and Double-Stranded RNA Viruses (pol). We show that the 180-kDa protein is formed by -1 ribosomal frame-shifting by a mechanism indistinguishable from that of retro-Viruses. Analysis of the "slippery site" suggests that a low probability of unpairing of the aminoacyl-tRNA from the 0-frame codon at the ribosomal A site reduces the efficiency of frameshifting more than the reluctance of a given tRNA to have its wobble base mispaired. Frameshifting of L-A requires a pseudoknot structure just downstream of the shift site. The efficiency of the L-A frameshift site is 1.8%, similar to the observed molar ratio in viral particles of the 180-kDa fusion protein to the major coat protein.
Jeremy A. Bruenn - One of the best experts on this subject based on the ideXlab platform.
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Genes from Double-Stranded RNA Viruses in the Nuclear Genomes of Fungi
Biocommunication of Fungi, 2012Co-Authors: Jeremy A. BruennAbstract:The sequencing of large numbers of eukaryotic genomes has demonstrated the widespread occurrence of viral genes in nuclear (and mitochondrial) genomes. Essentially all the families of RNA Viruses are represented, and we have coined the term NIRV (non-retroviral integrated RNA virus) for these sequences. Some 3% of sequenced eukaryotic genomes have NIRVs and the fungi are well represented with both complete and partial copies of RNA viral genes. The fungal NIRVs are the best characterized and demonstrate that, with the most widespread fungal Viruses, the dsRNA totiViruses and partitiViruses, which generally exist as stable persistent infections in their hosts, gene transfers between host and virus have taken place in both directions. Selection has preserved those events with adaptive value: hosts with NIRVs have become immune to infection with the cognate virus and Viruses with cellular toxin genes provide an advantage to their hosts by killing cells without the virus.
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A Second Double-Stranded RNA Virus from Yeast
Virology, 1996Co-Authors: Chung-mo Park, John D. Lopinski, Jenny Masuda, Tzy-hwa Tzeng, Jeremy A. BruennAbstract:Two Double-Stranded RNA Viruses exist as permanent persistent infections of the yeast Saccharomyces cerevisiae: ScVL1 and ScVLa. Both belong to the Totiviridae, which include a number of fungal and protozoan Double-Stranded RNA Viruses. Although ScVL1 and ScVLa share the same genomic organization and mode of expression and coexist in the same cells, they show no evidence of recombination: with one limited exception, sequence conservation is detectable only in regions conserved in all totiViruses. Both have two open reading frames on their single essential RNAs: cap (encoding a capsid polypeptide) and pol (encoding an RNA-dependent RNA polymerase). The ScVLa virus, like ScVL1, appears to express its Pol domain by a -1 translational frameshift.
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Interference with Replication of Two Double-Stranded RNA Viruses by Production of N-Terminal Fragments of Capsid Polypeptides
Virology, 1995Co-Authors: Wensheng Yao, Jeremy A. BruennAbstract:Abstract It is possible to interfere with the replication of a number of plant RNA Viruses by systemic production of viral capsid polypeptides or RNA-dependent RNA polymerases, or by production of untranslatable portions of viral plus strands or minus strands. Interference can occur by a number of mechanisms. We have discovered that the Saccharomyces cerevisiae Double-Stranded RNA Viruses ScVL1 and ScVLa, which exist as permanent persistent infections of their host cells, can be cured very efficiently by production of N-terminal fragments of their capsid polypeptides. These totiViruses produce only two polypeptides: a capsid polypeptide (Cap) and a Cap–Pol fusion polypeptide with RNA-dependent RNA polymerase activity. Three types of interference can be detected: interference due to overproduction of both Cap and Cap–Pol, interference due to overproduction of Cap (and consequent distortion of the Cap to Cap–Pol ratio), and interference due to negative complementation by N-terminal fragments of Cap. Some N-terminal fragments of Cap appear to be incorporated into viral particles, but only in the presence of a complete Cap protein. We postulate that incorporation of N-terminal fragments of Cap results in the formation of defective particles.
Bernard Delmas - One of the best experts on this subject based on the ideXlab platform.
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Analyses of the radiation of biRNAViruses from diverse host phyla and of their evolutionary affinities with other Double-Stranded RNA and positive strand RNA Viruses using robust structure-based multiple sequence alignments and advanced phylogenetic
BMC Evolutionary Biology, 2013Co-Authors: Jean-françois Gibrat, Mahendra Mariadassou, Pierre Boudinot, Bernard DelmasAbstract:Background BiRNAViruses form a distinct family of Double-Stranded RNA Viruses infecting animals as different as vertebrates, mollusks, insects and rotifers. With such a wide host range, they constitute a good model for studying the adaptation to the host. Additionally, several lines of evidence link biRNAViruses to positive strand RNA Viruses and suggest that phylogenetic analyses may provide clues about transition. Results We characterized the genome of a biRNAvirus from the rotifer Branchionus plicalitis . We used X-ray structures of RNA-dependent RNA polymerases and capsid proteins to obtain multiple structure alignments that allowed us to obtain reliable multiple sequence alignments and we employed “advanced” phylogenetic methods to study the evolutionary relationships between some positive strand and Double-Stranded RNA Viruses. We showed that the rotifer biRNAvirus genome exhibited an organization remarkably similar to other biRNAViruses. As this host was phylogenetically very distant from the other known species targeted by biRNAViruses, we revisited the evolutionary pathways within the BiRNAviridae family using phylogenetic reconstruction methods. We also applied a number of phylogenetic approaches based on structurally conserved domains/regions of the capsid and RNA-dependent RNA polymerase proteins to study the evolutionary relationships between biRNAViruses, other Double-Stranded RNA Viruses and positive strand RNA Viruses. Conclusions We show that there is a good correlation between the phylogeny of the biRNAViruses and that of their hosts at the phylum level using the RNA-dependent RNA polymerase (genomic segment B) on the one hand and a concatenation of the capsid protein, protease and ribonucleoprotein (genomic segment A) on the other hand. This correlation tends to vanish within phyla. The use of advanced phylogenetic methods and robust structure-based multiple sequence alignments allowed us to obtain a more accurate picture (in terms of probability of the tree topologies) of the evolutionary affinities between Double-Stranded RNA and positive strand RNA Viruses. In particular, we were able to show that there exists a good statistical support for the claims that dsRNA Viruses are not monophyletic and that Viruses with permuted RdRps belong to a common evolution lineage as previously proposed by other groups. We also propose a tree topology with a good statistical support describing the evolutionary relationships between the PicoRNAviridae , Caliciviridae , Flaviviridae families and a group including the Alphatetraviridae , Nodaviridae , Permutotretraviridae , BiRNAviridae , and Cystoviridae families.
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Analyses of the radiation of biRNAViruses from diverse host phyla and of their evolutionary affinities with other Double-Stranded RNA and positive strand RNA Viruses using robust structure-based multiple sequence alignments and advanced phylogenetic
BMC evolutionary biology, 2013Co-Authors: Jean-françois Gibrat, Mahendra Mariadassou, Pierre Boudinot, Bernard DelmasAbstract:Background BiRNAViruses form a distinct family of Double-Stranded RNA Viruses infecting animals as different as vertebrates, mollusks, insects and rotifers. With such a wide host range, they constitute a good model for studying the adaptation to the host. Additionally, several lines of evidence link biRNAViruses to positive strand RNA Viruses and suggest that phylogenetic analyses may provide clues about transition.
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crystal structure of an aquabiRNAvirus particle insights into antigenic diversity and virulence determinism
Journal of Virology, 2010Co-Authors: F Coulibaly, Christophe Chevalier, Bernard DelmasAbstract:Infectious pancreatic necrosis virus (IPNV), a pathogen of salmon and trout, imposes a severe toll on the aquaculture and sea farming industries. IPNV belongs to the AquabiRNAvirus genus in the BiRNAviridae family of bisegmented Double-Stranded RNA Viruses. The virions are nonenveloped with a T=13l icosahedral capsid made by the coat protein VP2, the three-dimensional (3D) organization of which is known in detail for the family prototype, the infectious bursal disease virus (IBDV) of poultry. A salient feature of the biRNAvirus architecture is the presence of 260 trimeric spikes formed by VP2, projecting radially from the capsid. The spikes carry the principal antigenic sites as well as virulence and cell adaptation determinants. We report here the 3.4-A resolution crystal structure of a subviral particle (SVP) of IPNV, containing 20 VP2 trimers organized with icosahedral symmetry. We show that, as expected, the SVPs have a very similar organization to the IBDV counterparts, with VP2 exhibiting the same overall 3D fold. However, the spikes are significantly different, displaying a more compact organization with tighter packing about the molecular 3-fold axis. Amino acids controlling virulence and cell culture adaptation cluster differently at the top of the spike, i.e., in a central bowl in IBDV and at the periphery in IPNV. In contrast, the spike base features an exposed groove, conserved across biRNAvirus genera, which contains an integrin-binding motif. Thus, in addition to revealing the viral antigenic determinants, the structure suggests that biRNAViruses interact with different receptors for attachment and for cell inteRNAlization during entry.
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Structure of biRNAvirus-like particles determined by combined electron cryomicroscopy and X-ray crystallography
Journal of General Virology, 2005Co-Authors: Joan Pous, Christophe Chevalier, Bernard Delmas, Malika Ouldali, Jorge Navaza, Jean LepaultAbstract:BiRNAViruses possess a capsid with a single protein layer in contrast to most Double-Stranded RNA Viruses infecting multicellular eukaryotes. Using freeze-drying and heavy metal shadowing, the capsids of two biRNAViruses, infectious bursal disease virus (IBDV) and infectious pancreatic necrosis virus, as well as of an IBDV virus-like particle (VLP) are shown to follow the same T=13 laevo icosahedral geometry. The structure of the VLP was determined at a resolution of approximately 15 A ° (1?5 nm) by a combination of electron cryomicroscopy and a recently developed three-dimensional reconstruction method, where the scattering density is expressed in terms of symmetry-adapted functions. This reconstruction methodology is well adapted to the icosahedral symmetry of Viruses and only requires a small number of images to analyse. The atomic model of the exteRNAl capsid protein, VP2, recently determined by X-ray crystallography, fits well into the VLP reconstruction and occupies all the electron densities present in the map. Thus, similarly to the IBDV virion, only VP2 forms the icosahedral layer of the VLP. The other components of both VLP and IBDV particles that play a crucial role in the capsid assembly, VP1, VP3 and the peptides arising from the processing of pVP2, do not follow the icosahedral symmetry, allowing them to be involved in other processes such as RNA packaging.
José R Castón - One of the best experts on this subject based on the ideXlab platform.
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structure of dsRNA mycoViruses
2020Co-Authors: José R Castón, Nobuhiro Suzuki, Said A GhabrialAbstract:Abstract Most fungal, Double-Stranded RNA Viruses lack an extracellular phase in their life cycles and are transmitted by cytoplasmic interchange. DsRNA mycovirus capsids are based on a 120-subunit T=1 capsid, with a dimer as the asymmetric unit. These capsids, which remain structurally undisturbed throughout the viral cycle, are, nevertheless, dynamic assemblies that mediate multiple activities such as the organization of the viral genome and the viral polymerase necessary for RNA synthesis. Within the capsid, fungal dsRNA Viruses show a low degree of genome compaction compared to reoViruses, and contain 1–2 copies of the RNA-polymerase complex per virion.
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The biological attributes, genome architecture and packaging of diverse multi-component fungal Viruses.
Current opinion in virology, 2018Co-Authors: Yukiyo Sato, José R Castón, Nobuhiro SuzukiAbstract:Many fungal Viruses or mycoViruses have multi-segmented, rather than single-segmented, genomes. This multi-segment nature is frequently possessed by Double-Stranded RNA Viruses, which include members of the Chrysoviridae, Quadriviridae, MegabiRNAviridae, Partitiviridae, and Reoviridae families, and unassigned groups. Their genome segments are often packaged separately with the exception of mycoreoViruses, which are multi-segmented but mono-particulate Viruses. These multi-segmented fungal dsRNA Viruses, as exemplified by reoViruses, have been extensively studied among structural biologists, and contributed to discoveries of novel virion structures. Multi-component systems, interactions of Viruses with subviral agents such as satellite and defective RNAs as typified by the yeast killer, and the rule-breaking neo-virus lifestyle exhibited by a capsidless single-stranded RNA virus hosted in an unrelated Double-Stranded RNA virus are also discussed. Fungal multi-segmented Viruses and multicomponent virus systems would continue to provide virologists with interesting future challenges.
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cryphonectria nitschkei virus 1 structure shows that the capsid protein of chrysoViruses is a duplicated helix rich fold conserved in fungal double stranded RNA Viruses
Journal of Virology, 2012Co-Authors: Josue Gomezblanco, José L. Carrascosa, Daniel Luque, Wendy M Havens, Benes L. Trus, Carlos Alfonso, Said A Ghabrial, Jose M Gonzalez, José R CastónAbstract:Cryoelectron microscopy reconstruction of Cryphonectria nitschkei virus 1, a Double-Stranded RNA (dsRNA) virus, shows that the capsid protein (60 copies/particle) is formed by a repeated helical core, indicative of gene duplication. This unusual organization is common to chrysoViruses. The arrangement of many of these putative α-helices is conserved in the totivirus L-A capsid protein, suggesting a shared motif. Our results indicate that a 120-subunit T=1 capsid is a conserved architecture that optimizes dsRNA replication and organization.
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three dimensional structure and stoichiometry of helmintosporium victoriae190s totivirus
Virology, 2006Co-Authors: José R Castón, Padmanaban Annamalai, José L. Carrascosa, German Rivas, Daniel Luque, Benes L. Trus, Carlos Alfonso, Jose M Gonzalez, Said A GhabrialAbstract:Most Double-Stranded RNA Viruses have a characteristic capsid consisting of 60 asymmetric coat protein dimers in a so-called T = 2 organization, a feature probably related to their unique life cycle. These capsids organize the replicative complex(es) that is actively involved in genome transcription and replication. Available structural data indicate that their RNA-dependent RNA polymerase (RDRP) is packaged as an integral capsid component, either as a replicative complex at the pentameric vertex (as in reovirus capsids) or as a fusion protein with the coat protein (as in some totivirus). In contrast with members of the family Reoviridae, there are two well-established capsid arrangements for dsRNA fungal Viruses, exemplified by the totiViruses L-A and UmV and the chrysovirus PcV. Whereas L-A and UmV have a canonical T = 2 capsid, the PcV capsid is based on a T = 1 lattice composed of 60 capsid proteins. We used cryo-electron microscopy combined with three-dimensional reconstruction techniques and hydrodynamic analysis to determine the structure at 13.8 A resolution of Helminthosporium victoriae 190S virus (Hv190SV), a totivirus isolated from a filamentous fungus. The Hv190SV capsid has a smooth surface and is based on a T = 2 lattice with 60 equivalent dimers. Unlike the RDRP of some other totiViruses, which are expressed as a capsid protein-RDRP fusion protein, the Hv190SV RDRP is incorporated into the capsid as a separate, nonfused protein, free or non-covalently associated to the capsid interior.
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fungal virus capsids cytoplasmic compartments for the replication of double stranded RNA formed as icosahedral shells of asymmetric gag dimers
Journal of Molecular Biology, 1994Co-Authors: Holland R Cheng, José R Castón, Benes L. Trus, Guo Ji Wang, Fei Gu, Thomas J Smith, Timothy S Baker, Robert F Bozarth, Naiqian Cheng, Reed B. WicknerAbstract:Abstract The primary functions of most virus capsids are to protect the viral genome in the extra-cellular milieu and deliver it to the host. In contrast, the capsids of fungal Viruses, like the cores of all other known double stranded RNA Viruses, are not involved in host recognition but do shield their genomes, and they also carry out transcription and replication. Nascent (+) strands are extruded from transcribing virions. The capsids of the yeast virus L-A are composed of Gag (capsid protein; 76 kDa), with a few molecules of Gag-Pol (170 kDa). Analysis of these 420 A diameter shells and those of the fungal P4 virus by cryo-electron microscopy and image reconstruction shows that they share the same novel icosahedral structure. Both capsids consist of 60 equivalent Gag dimers. whose two subunits occupy non-equivalent bonding environments. Stoichiometry data on other Double-Stranded RNA Viruses indicate that the 120-subunit structure is widespread, implying that this molecular architecture has features that are particularly favorable to the design of a capsid that is also a biosynthetic compartment.