Pretend that you setup an experiment to study the gene expression of HSV-1. You
ID: 216927 • Letter: P
Question
Pretend that you setup an experiment to study the gene expression of HSV-1. You infect 4 dishes of a permissive cell line with this virus. You add 3 different inhibitors during the infection. Drug A prevents all host cell translation. Drug B inhibits viral DNA replication. Drug C prevents the assembly of viral capsids. You then measure how much viral mRNA is synthesized from 3 different viral genes. See the table below of the results: Inhibitor 3. Viral gene #1 Viral gene #2 Viral gene #3 None (control) "+" signifies the relative amount of viral mRNA transcribed at each time point ".-" means that no viral mRNA was detected in that condition (a) At what time point do you think each viral gene is synthesized during the infection cycle of HSV? (Note: you do not need to give an actual time (such as hours,) just the name of the class of gene.) [6 pts.] Viral gene #1 : Viral gene #2: Viral gene #3 (b) why does drug A not prevent transcription from viral gene #1? Explain. [4 pts.]Explanation / Answer
Please find the answers below:
Answer a: Viral gene expression takes place in a different manner as compared to normal gene expression. Firstly, the viral RNA is converted into cDNA by the action of reverse transcriptase and this cDNA is converted into mRNA by host-cell machinery. Thus, any drug which prevents the activity of host-cell transcription and translation would sequentially prevent viral mRNA synthesis. Hence, the drug A prevents host-cell translation thus would have minimized effect on viral mRNA transcription and translation. Drug B having preventive effect on viral DNA replication would be even slower in nature. Finally, drug C having preventive effect on viral capsid protein assembly would have even slower effect since viral capsid assembly is the last phase of viral assembly. .
Hence, the viral gene A is a late acting gene since it is expressed in all drug incubations. Following gene A comes gene B and finally, gene C. Thus, gene C is an early expression protein followed by gene B and finally gene A is a late-expression protein.
Answer b: According to the information, the durg A prevent all host-cell translation. It must be carefully noted here that viral translational machinery can be independent of the host-cell translation machinery. Thus, this clearly suggests that this virus HSV-1 contains its own translational machinery which in non-responsive to this drug A and hence translation continues even when drug is applied to the system.
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