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 The reovirus virion.

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

11. Genome
Fig 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 Stepwise disassembly of reovirus.

15. Genes and proteins
Enzymes in the viral core synthesize and cap messenger RNAs
Messenger RNA synthesis.
l3, m 2 at l2 spikes
Messenger RNA capping.
l2 spike protein
Messenger RNA export.
Fig 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 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 CDK by s1s

21. Key Terms Jaundice Adherens junction
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
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