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Exploring Reoviruses: Genomic Composition and Distinctive Characteristics

Discover the fascinating features of Reoviruses, from their segmented genome to unique protein synthesis processes. Learn about the variety of diseases they cause and the diverse hosts they infect. Uncover the distinctive characteristics that set Reoviruses apart in the viral world.

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Exploring Reoviruses: Genomic Composition and Distinctive Characteristics

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  1. Reoviruses - Reoviridae Virion Genome Genes and proteins Viruses and hosts Diseases Distinctive characteristics

  2. Reoviruses - Reoviridae • Virion • Naked icosahedral capsid • Diameter 60–85 nm. • Capsid consists of two or three concentric protein shells. • Inner capsid, or core, contains RNA polymerase and capping enzymes.

  3. Reoviruses - Reoviridae • Genome • Linear ds RNA. • 10–12 segments. • Total genome length 18–24 Kb.

  4. Reoviruses - Reoviridae • Genes and proteins • mRNAs are full-length copies of each genome segment. • Typically one protein encoded per genome segment. • Six–eight capsid proteins. • Three–six nonstructural proteins.

  5. Reoviruses - Reoviridae • Viruses and hosts • Twelve genera, including Orthoreovirus, Rotavirus, Orbivirus. • Infect humans (reoviruses types I–III, rotaviruses, Colorado tick fever virus), mammals, birds, fish, mollusks, plants, insects, and fungi.

  6. Reoviruses - Reoviridae • Diseases • Members of genus Orthoreovirus cause little or no disease in humans. • Rotavirus gastroenteritis is an important cause of infant disease in the developed world and • infant mortality in the developing world. • Viruses spread between hosts by direct transmission, contaminated food or water, or arthropod vectors.

  7. Reoviruses - Reoviridae • Distinctive characteristics • Family has members that infect a broad range of hosts from fungi to humans. • mRNAs are synthesized and capped inside intact cores and extruded through channels into the cytosol. • Synthesis of double-stranded genome RNAs occurs within core-like subvirion particles. • A single copy of each gene segment is packaged into each virion by an unknown sorting mechanism. • Gene segments can be reassorted during coinfection of cells by different strains.

  8. Virion • Reoviruses were the first double-stranded RNA viruses discovered

  9. Virion • Reoviridae have segmented genomes made of double-stranded RNA Fig. 24.1 The reovirus virion.

  10. Virion • Reoviridae have segmented genomes made of double-stranded RNA Fig. 24.2 Generation of reassortant viruses.

  11. Genome Fig. 24.3 Features of reovirus gene segments.

  12. Genes and proteins • Reovirus virions contain concentric layers of capsid proteins

  13. Genes and proteins • The attachment protein binds to one or two cellular receptors

  14. Genes and proteins • The attachment protein binds to one or two cellular receptors • from virions and the core is released into the cytoplasm Fig. 24.4 Stepwise disassembly of reovirus.

  15. Genes and proteins • Enzymes in the viral core synthesize and cap messenger RNAs • Messenger RNA synthesis. • l3, m 2at l2 spikes • Messenger RNA capping. • l2 spike protein • Messenger RNA export. Fig. 24.6 Synthesis of reovirus messenger RNAs.

  16. Genes and proteins • Translation of reovirus mRNAs is regulated • Not all reo virus proteins are produced in the same amount • The length of mRMA • Sequences around AUG • Difference in the length of 5’ UTR • NSP3 binds 3’ end of mRNA and also 5’ cap complex • functionally replace PABP for efficient translation

  17. Genes and proteins • Interferon and PKR: effects on viral and cellular protein synthesis • The s3 protein modulates PKR activation. • Binds to ds RNA, competing with PKR • PKR regulation and cancer. • Replicates more efficiently in transformed cells • Acitivated Ras signal interferes with PKR function • Might be useful as novel oncolytic agents

  18. Genes and proteins • Synthesis of progeny double-stranded genomes occurs within subviral particles • Virus factories. • Intracytoplasmic inclusions • Replicase particles. • Secondary transcription and encapsidation. Fig. 24.8 Assortment of gene segments and virion assembly.

  19. Genes and proteins • Reoviruses induce apoptosis via activation of transcription factor NF-B • Receptor binding and apoptosis. • Binding to sialic acid and JAM-A is required for maximal levels of apoptosis • Cell-cycle arrest. • Arrest G2/M transition • Due to hyperphosphorylation and activation of CDKby s1s

  20. Adherens junction Apoptosis Caspases Cathepsins Cryoelectron microscopy Cyclin-dependent kinase (CDK) Double-stranded RNA-dependent protein kinase (PKR) Encephalitis Ependymal cells Hydrocephalus Inclusion bodies Infectious subvirion particles (ISVPs) Interferons Jaundice Junctional adhesion molecule A (JAM-A) Myocarditis Nectins NF-kB (nuclear factor-kB) 2’, 5’-oligo(A) synthetase Oncolytic Ras Reassortant viruses Ribonuclease L Sialic acid Tight junction Tropism Key Terms

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