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Virology 1.2: Spring, 2014. Components of a virus and some definitions. Virion -an individual virus particle (on the left). Minimal virion. Essential components (not necessarily the only ones) Capsid (the cargo container) Genome (the cargo). Two simple examples of capsids.

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Virology 1.2: Spring, 2014


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    1. Virology 1.2: Spring, 2014 Components of a virus and some definitions

    2. Virion-an individual virus particle (on the left)

    3. Minimal virion • Essential components (not necessarily the only ones) Capsid (the cargo container) Genome (the cargo)

    4. Two simple examples of capsids Rod-shaped and isometric

    5. Some characteristics of genomes • DNA or RNA • Single or double stranded (ss or ds) • Linear or circular • Haploid or diploid

    6. Some more characteristics of genomes • Size and genetic content varies • One or more pieces of nucleic acid (aka multipartite or segmented genome) • May have genome-linked protein or VpG • May be (+) or (-) sense or ambisense

    7. RNASecondaryStructure

    8. Viral Nucleic Acids Have Secondary Structure Predicted Structure of Uncoated NS1 RNA from Influenza A H5N1 Left: Swine Right: Duck Citation:Pallavi S, Vijai S, M Arshad (2008) Modeling of RNA Secondary Structure of Non Structural Gene and Evolutionary Stability of the Influenza Virus Through In Silico Methods. J Proteomics Bioinform 1: 219-226. doi:10.4172/jpb.1000026

    9. Some characteristics of capsids • Multiple copies of capsid protein • Capsid protein is aka the structural subunit of the capsid • May be more than one type of capsid protein in the capsid • A capsid protein may be a lipo- or glycoprotein

    10. Some more complex views of isometric capsids

    11. Double layer capsids • Human rotavirus- a reovirus

    12. Geminiviruses Contains one small DNA molecule in each twin capsid

    13. Virions may contain additional components • Envelope or membrane • Host-derived • Membrane proteins • Complex virions may have more than one membrane

    14. Features of enveloped virions Influenza A, an Orthomyxovirus Membrane and membrane proteins SARS virus - a coronavirus

    15. Segmented genome Orthomyxovirus on right

    16. Other components • Matrix (layer inside envelope) • Tegument (herpesviruses only) • Core or nucleocapsid

    17. Herpesvirus virion • Human herpesvirus 1 (HHV-1) aka herpes simplex virus 1

    18. Virion may contain other proteins • Non-structural proteins • Regulatory proteins • Enzymes required for viral replication

    19. Non-genomic nucleic acids • Primers for replication • tRNAs in retroviruses

    20. Features of more complex capsids • Adenovirus

    21. A highly complex and functional capsid • Bacteriophage T4-a myovirus

    22. Tails-Another interesting feature Phage lambda and its relatives, the siphoviruses Corndog phage-a mycobacteriophage

    23. Bacilliform capsids Rabies virus – a Rhabdovirus

    24. Core of HIV-1 Diagnostic shape “Core” is actually the virus capsid

    25. Multicomponent viruses • Aka multipartite viruses or coviruses • Segmented genome viruses in which the genome segments are distributed among more than one particle • Usually plant viruses

    26. Defective/helper viruses • Defective virus cannot complete “life” cycle • Helper virus provides missing functions • Complementation • May or may not be related viruses • Defective interfering (DI) particles are different and are usually laboratory artifacts (next!)

    27. Defective Interfering (DI) Particles Defective Interfering particles originate from parental viruses by deletions of the viral genome and subsequent evolution for replication fitness of the defective particle. DI particles compete with the competent, parental virus.

    28. Satellite virus(definition from Field’s Virology) • Type of defective virus • Stable ecological relationship • Satellite (of) tobacco necrosis virus • STNV • Replication-defective • But competent for capsid protein • Minimal identity

    29. Satellite nucleic acid (RNA) • Helper provides capsid • Satellite may provide some of own replication functions or part of its own core • Hepatitis delta agent aka HDV CMV Associated RNA 5 aka CARNA5 (satellite RNA may change symptoms)

    30. Satellite Viruses and Satellite RNAs Both are defective!!! Satellite RNAs Packaged in the coat protein of the helper Virus. Satellite viruses Encode a coat protein that encapsidates the Satellite Genome. Satellite RNAs: Satellite RNAs are small RNA molecules that require a host virus for replication. They may or may not reduce the titer of the host virus. Satellite RNAs ranges from 200 to 1700 nt. Larger satellite RNAs may encode a protein (not capsid). Satellite viruses: Defective viruses which can multiply only by association with a helper virus which complements the defective gene. Satellite viruses may be associated with certain plant viruses, animal viruses, or bacteriophages. They differ from satellite RNA (RNA, satellite) in that satellite viruses encode their own coat protein.

    31. Tobacco mosaic virus and a satellite

    32. Satellites never found without helper But helper may be found without satellites

    33. Virophages • Look like a cross between a satellite virus and a bacteriophage • dsDNA agents with ~20 kbp genome • Only found associated with giant viruses of protozoa • “Sputnik”, “Maverick”

    34. Viroids • Infectious RNAs-no capsids whatsoever • Small • Ss • Circular • Infect plants • Not defective, not satellites-they are different entities!

    35. Avocado sunblotch viroid infection of avocado

    36. Provirus or prophage • Viral genome inserted (integrated) into host genome • Lambda forms a prophage, retroviruses form proviruses

    37. Prions Scrapie—Germany (1759) “Some sheep also suffer from scrapie, which can be identified by the fact that affected animals lie down, bite at their feet and legs, rub their backs against posts, fail to thrive, stop feeding and finally become lame. They drag themselves along gradually become emaciated and die. Scrapie is incurable. The best solution, therefore, is for a shepherd who notices that one of his animals is suffering from scrapie, to dispose of it quickly and slaughter it away from the manorial lands for consumption by the servants of the nobleman. A shepherd must isolate such an animal from healthy stock immediately because it is infectious and can cause serious harm to the flock.”

    38. Prion particles • Proteinaceous infectious particle • No detectable nucleic acid • Can it really replicate? • Stanley Prusiner, 1982 • Prions are not viruses

    39. Some prion diseases

    40. Retroid family • Reverse transcriptase step • Some “true viruses” included such as HIV or cauliflower mosaic virus • Retrotransposons, some introns

    41. Some Controversial Terms to be Avoided Virusoid - has no recognized meaning Slow virus – historical, old-fashioned, archaic term, not a lentivirus