06 Chapter 33 Herpesvirus.ppt - Herpesviruses Chapter 33...

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Herpesviruses Chapter 33
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Properties of Herpesviruses Structure and Composition Spherical iscoahedron, 150-200 nm Double-stranded DNA, linear More than 35 proteins Enveloped Replication from nucleus (budding) Features Encode many enzymes Establish latent infections Lifelong persistence Significant cause of death in immunocompromised hosts Some can cause cancers
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Properties of Herpesviruses Classification (human viruses) Subfamilies Alpha Beta Gamma Species Simplex 1 (HHV-1) (alpha) Simplex 2 (HHV-2) (alpha) Varicella (HHV-3) (alpha) Epstein-Barr (HHV-4) (gamma) Cytomegalovirus (HHV-5) (beta) HHV-6 (beta) HHV-7 (beta) Kaposi’s sarcoma virus (HHV-8) (gamma)
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Properties of Herpesviruses Replication of HSV Virus attachment and membrane fusion Viral host shutof (VHS) protein released into the cytoplasm and initiates the degradation of host cell mRNA α-Trans-inducing factor (αTIF) is transported to the nucleus Capsid travels to nucleus where viral DNA is released, enters a nuclear pore and circularizes αTIF induces the expression of viral alpha genes The mRNAs for the alpha genes are translated on ribosomes The proteins then enter the nucleus and express the viral beta genes The beta proteins are involved in degrading cellular chromatin and localizing cellular DNA to the inner side of the nuclear envelope ( margination ) Viral DNA is replicated as concatemers Gamma proteins (structural) are expressed Capsid proteins self assemble and DNA concatemers are cleaved and packaged into capsids
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Properties of Herpesviruses Replication of HSV (cont.) Nuclear escape Viral proteins induce budding of the capsid through both nuclear membranes Thus, capsid escapes into the cytoplasm Viral proteins associate with the cellular vesicles These proteins have affinity for the capsid proteins and cause the vesicle to wrap around the virus , providing it with an double-layered envelope Virus traverses the ER then Golgi prior to release from the cell The outer membrane fuses with the plasma membrane
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Herpesvirus Diseases Herpes Simplex viruses Two species HSV-1: oropharyngeal sores (children) HSV-2: genitalia (young adults) Highly similar genomes, but distinct 150 kb 70+ polypeptides Virulence factors gC binds complement C3b gE is an Fc receptor for IgG
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Herpes simplex viruses (cont.) Pathology Wide cellular tropism Most common to dermal tissues (herpetic lesions) Cell fusion followed by cell lysis Inflammatory response
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