Togaviruses -Togaviridae
Togaviruses -Togaviridae Virion - Spherical enveloped particle with a fringe of projections.
- Diameter 70 nm.
- Nucleocapsid has icosahedral symmetry (T = 4).
- Envelope glycoproteins also arranged with icosahedral symmetry, T = 4.
Togaviruses - Togaviridae Genome - Linear ss RNA, positive sense.
- Alphaviruses: 11 Kb; rubella virus: 9 Kb.
- 5 end is capped and methylated.
- 3 end has a 70-nt poly(A) tail.
Togaviruses - Togaviridae - Four nonstructural proteins (for viral RNA synthesis) translated directly from genome RNA.
- Five structural proteins (one capsid protein, three envelope proteins, a small hydrophobic protein) translated from a subgenomic mRNA.
Togaviruses - Togaviridae - Two genera: Alphavirus (27 members) and Rubivirus (rubella virus).
- Alphaviruses (Sindbis, Semliki Forest, Ross River) infect birds and mammals.
- Most alphaviruses are transmitted by mosquitoes.
Togaviruses - Togaviridae Diseases - Symptoms include fever, rash, arthritis, and encephalitis; can be fatal.
- Rubella infection (German measles) can lead to fetal abnormalities.
Togaviruses - Togaviridae Distinctive characteristics - A subgenomic mRNA codes for virion structural proteins.
- Structural proteins are synthesized as a polyprotein that undergoes cleavage and membrane association.
- RNA replication is associated with cytoplasmic membranes.
- Alphaviruses have the unusual ability to replicate in both invertebrate and vertebrate hosts.
- Lipid envelope derived from the plasma membrane (vertebrate cells) or internal membranes (insect cells).
Virion Most togaviruses are arthropod borne, transmitted between vertebrate hosts by mosquitoes
Virion
Virion Togaviruses enter cells by low pH-induced fusion inside endosome vesicles Nonstructural proteins are made as a polyprotein that is cleaved by a viral protease
Genes and proteins
Genes and proteins Partly cleaved nonstructural proteins catalyze synthesis of full-length antigenome RNA
Genes and proteins
Genes and proteins Structural proteins are cleaved during translation and directed to different cellular locations
Genes and proteins
Genes and proteins Effects of mutations in viral proteins on cytopathic effects and on pathogenesis - nsP2 mutation decreases viral RNA systhesis
- Do not cause cytopathic effect
Genes and proteins Alphaviruses have been modified to serve as vectors for the expression of heterologous proteins Alphavirus vectors have multiple potential uses - Express proteins of unrelated viruses
- Express proteins toxic to insects
Genes and proteins
Key Terms Antigenome Apoptosis Arthropod-borne viruses -galactosidase Chloramphenicol acetyltransferase Cytopathic Encephalitis Furin protease Green fluorescent protein Heparan sulfate Hippocampus Interferon
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