1. Shortly after the discovery of positive-sense RNA viruses such as poliovirus,
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1. Shortly after the discovery of positive-sense RNA viruses such as poliovirus, researchers attempted to discover more about the mechanisms of how these viruses replicated their genomes. A famous virologist named David Baltimore made a crucial discovery in this field by making use of a drug inhibitor called Actinomycin D. This molecule can be used in the laboratory to inhibit the synthesis of cellular mRNA transcription (a) If this drug was added to poliovirus-infected cells, what do you suppose would happen to viral RNA synthesis and genome replication Explain your reasoning. [2 pts.] viral RNA synthesis and genome replication Explain your reasoning. [2 pts.] viral RNA synthesis and genome replication Explain your reasoning. [2 pts.] (b) If this drug was added to reovirus-infected cells, what do you suppose would happen to (c) If this drug was added to herpesvirus-infected cells, what do you suppose would happen toExplanation / Answer
(a) Actinomycin prevents synthesis of viral RNA by affecting a stage of growth that occurs after penetration.
After penetration the genomic RNA is a template for RNA genome replication.
At a certain concentration actinomycin D inhibits the cellular RNA synthesis. The polymerase production was also inhibited by inhibiting the formation of RNA polymerase. Actinomycin D interferes with the kinetics and ultimate level of polymerase formation to the same extent in both cell growth and minimal media.
(b) Reoviruses are the double- stranded RNA viruses.
In the presence of actinomycin D the growth of reovirus can be inhibited.
The virus enters by attachment and undergoes endocytosis and then proteolysis by generating infectious subvirion particles. These viral proteins allows the mRNA transcription.
The viral particles has a necessary machinery to synthesize mRNA's. A RNA polymerase complex composed of 3 different molecules is present.
Actinomycin D shows a greater effect on double stranded RNA than single stranded polio virus.
The inhibition of mRNA synthesis is occured with the addition of this drug by inhibiting the RNA polymerase complex.
(c) Herpes virus enters by attachment and then by direct fusion into the body, by a microtubule mediated transport.
The transcription or replication occurs in the nucleus.
This is a DNA virus. The linear DNA is converted into circular DNA and the transcription occurs by certain factors UL9, UL29, UL30 which acts as a DNA polymerase and UL42.
When Actinomycin D is added it prevents the viral gene expression by blocking the UL30 factor and blocks the genome replication.
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