Virology Unit 4

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tapper1808
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144042
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Virology Unit 4
Updated:
2012-04-02 19:41:47
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Chapter expression replication viral genome eukaryotic hosts RNA viruses
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Chapter 4
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  1. (+) ssRNA
    • 1. Make proteins from the single RNA strand
    • 2. Make new RNA using the single strand RNA as a template
    • 3. Host-cell machinery or processes must be modified.
    • 4. Eukaryotic cells do not have the ability to synthesize RNA using an RNA template.
    • 5. RNA viruses must provide RNA-dependent-RNA-polymerase (replicase)
  2. (-)ssRNA
    • 1. Make mRNA from genomes before it can be expressed
    • 2. Create proteins from newly formed mRNA
    • 3. Host-cell machinery or processes must be modified.
    • 4. Eukaryotic cells do not have the ability to synthesize RNA using an RNA template.
    • 5. RNA viruses must provide RNA-dependent-RNA-polymerase (replicase)
  3. dsRNA
    Create a double stranded copy and insert it into the host-cell genome.
  4. Eukaryotic translation (mRNA)
    • Monisistronic- one gene on protein
    • Addition of polyadenosine (poly-A) tail at 3' end
    • Addition of 7-methyl-guanosine (7mG) cap at 5' end
    • Non-coding introns spliced out
    • Coding exons brought together
    • mRNA transported from nucleus to cytoplasm then translated.
    • Sythesized protein may be processed into active form by cleavages, phosphorylations, of glycosylations.
  5. Phosphorylation
    Phosphorylation is the addition of a phosphate (PO43-) group to a protein or other organic molecule.

    Many enzymes and receptors are switched "on" or "off" by phosphorylation and dephosphorylation.

    The addition of a phosphate (PO4) molecule to a polar R group of an amino acid residue can turn a hydrophobic portion of a protein into a polar and extremely hydrophilic portion of molecule.
  6. Glycosylation
    Enzymatic process that attaches glycans to proteins, lipids, or other organic molecules.

    A form of co-translational and post-translational modification.

    Glycans serve a variety of structural and functional roles in membrane and secreted proteins.
  7. Poliovirus
    • Picornaviridae
    • Enterovirus (also hapatitis A)
    • Class IV= (+)RNA
    • Icasahedral head
    • No envelope
  8. Picornaviridae
    • Enteroviruses: poliovirus, hepatitis A
    • Rhinoviruses
    • Poly A ail
    • No 5' cap; has VPg protein instead
  9. What is VPg?
    • Protein attached to 5' end of RNA during synthesis of Picornaviridae.
    • VPg=viral protein genome-linked.
    • 3CDpro (a protease) cleaves VPg from membrane-bound 3AB.
    • 3Dpol (picornavirus RNA polymerase) then synthesizes VPg-pUpU using the sequence AAACA from the cre (cis-acting replication element) of the template strand.
    • 3Dpol-VPg-pUpU complex moves to 3' poly(A) tail of template strand.
    • RNA synthesized using the pUpU sequence as a primer.
  10. How is VPg attached?
    3CDpro (a protease) cleaves VPg from membrane-bound 3AB. 3Dpol (picornavirus RNA polymerase) then synthesizes VPg-pUpU using the sequence AAACA from the cre (cis-acting replication element) of the template strand. The 3Dpol-VPg-pUpU complex then moves to the 3' poly(A) tail of the template strand and commences RNA synthesis using the pUpU sequence as a primer.
  11. Sindbis virus
    • Togaviridae
    • Icosahedral nucleocapsid
    • Enveloped with spikes
    • Class IV= (+)RNA
    • 5' cap; poly A tail
  12. Togaviridae
    • Icosahedral nucleocapsid
    • Enveloped with spikes
    • Class IV= (+)RNA5' cap; poly A tail

    Includes: Sindbis virus, alphaviruses, rubella virus, pestiviruses
  13. Murine hepatitis virus (MHV)
    • Coronaviridae
    • Helical nucleocapsid
    • Enveloped
    • Class IV= (+)RNA
    • 5' cap; 3' poly A tail
  14. Coronaviridae
    • Helical nucleocapsid
    • Enveloped
    • Class IV= (+)RNA
    • 5' cap; 3' poly A tail

    Includes: MHV
  15. Picornavirus translation
    • Entire genome translated fron initiation site.
    • Single polyprotein of 247 kdaltons cleaved during synthesis (nascent cleavage).
    • Structural->cleavage->synthesis proteins.
  16. nascent cleavage
    Cleavages occuring while protein is being (synthesized) "born".
  17. Picornavirus (poiovirus) nascent cleavage to create individual proteins
    • First 4 genes for capsid, together in a block
    • 1st cleavage makes P1: 4 capsid proteins (1A, 1B, 1C, 1D)
    • Autocatalytic by 2A at tyrosine-glycine site.
    • Remaining genes, two sets, code proteins for cleavage and synthesis. P2 (2A, 2B, 2c) and P3 (3A, 3B, 3C, 3D)
    • Other cleavage by 3C, glutamine-glycine specific.
  18. Poliovirus (Picornavirus) prevents host mRNA translation
    • Host mRNA recognized by cap-binding complex, eIF4G.
    • Poliovirus protein 2A activates host protease.
    • Protease cleaves cap.
    • Host cell mRNA cannot be recognized.
  19. How is poiliovirus translation begun
    • Genome has long untranslated sequence at 5' end forming series of hairpin loops.
    • They block ribosome scanning looking for 1st AUG start codon.
    • At end of leader, sequence (IRES) facilitates formation of translation initiation complex at an internal location.
  20. IRES
    Internal Ribosomal Entry Site
  21. How does poliovirus replicate genome
    • Replication polyproteins needed in P3 go thru cleavage.
    • 3AB protein becomes associated with cell membrane.
    • 3CD and host cell PCBP (polyC binding protein) interact with 5' end.
    • 3CD transfers UMPs to 3AB then 3C cleaves it forming VPg-pUpU-OH.
    • 3CD cleaved at same time, RNApolymerase 3D from protease 3C.
    • VPg primer and 3D polymerase then bind to poly A tail.
  22. UMPs
    Uridine monophosphate, also known as 5'-uridylic acid and abbreviated UMP, is a nucleotide that is used as a monomer in RNA.
  23. AMPs
    Adenosine monophosphate (AMP), also known as 5'-adenylic acid, is a nucleotide that is used as amonomer in RNA.
  24. Togavirus
  25. (-)RNA features
    • common features suggest ancestral "progenitor"
    • Flexible nucleocapsids with helical symmetry
    • Single stranded RNA genome
    • Enveloped with spikes
    • Genome cannot serve as template for translation
    • No cap or tail

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