Nucleus must have virion rna dependent rna polymerase

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nucleus) must have virionRNA-dependent RNA polymerase in order to synthesize mRNA. OncogenicTransformation: viral DNA is integrated into host DNA, where it interferes with host mechanisms, drives division, but does not produce an infective virus. SV40 (polyomavirus) is capable of oncogenictransformation. Selective pressure is directed at viral surface proteins, driving evolution into type-specific proteins. Internal epitopes, on the Bases for Viral Classification Host range Disease characteristics Mode of transmissionPhysical characteristics Properties of the virionViruses contain many genes are devoted to preventing destruction In an enveloped virus, glycoproteinsin the viral envelope mediate attachment and entry into host cells. In a nonenvelopedvirus, proteins in the capsidmediate attachment and entry into the host cell. Specialized capsidproteins Example:adenovirus fiber segment of the viral genome to encode more than one viral proteinAttachmentMediated by interaction beweenvirus attachment proteins and host cell receptors, attachment determines cell tropism and host range Penetration Surface glycoproteinson the viral envelope mediate fusion. Glycoproteinsthat operate at neutral pH mediate viral entry at the cell surface. Those that function at low pH mediate endosomalfusion. UncoatingmRNA synthesis Protein synthesis Viruses have proteases that cleave cap-binding protein such that the ribosomespreferentially translate the uncapped RNA of the viruses. Viral mRNA is monocistronic. Protease is required to produce individual protein components. Assembly Egress Budding, which requires viral proteins, permits virus production without cell lysis. Extracellular survival proteins. Internal epitopes, on the other hand, are not subject to the same pressures and are group specific. •Virus infects without apparent symptoms until about 14 days later when the immune response is activated. The viral titer quickly drops. •These infections require a large reservoir in order to persist •Examples: cold, polio, measles, mumps, rubella Hit-and-Run Infections•The infection is not eradicated by the immune response. Small amounts of virus trickle out all the time. •Can infect isolated populations •Example: HSV Persistent Infections •The viral titer drops to very low levels, but can recur. •Example: varicellazoster virus Latent Infection devoted to preventing destruction of infected cells. These genes target apoptotic and immune recognition pathways. Determinants of Virus-Cell interaction•Receptors are required for a virus to attach and enter the host cell. Host cells with the appropriate receptors are susceptible. Those that lack receptors are resistant. •Cellular factors (level of differentiation, dividing/non-dividing state) determine whether a host cell is permissive (enables virus to undergo its life cycle) or non-permissive and whether the infection is productive or abortive.

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