Suppose you were studying retroviral reverse transcription, and you were interes

Question

Suppose you were studying retroviral reverse transcription, and you were interested in developing an in vitro system (test-tube enzymatic reaction in the absence of cells) for studying this process. You purify reverse transcriptase and its associated RNase H activity, and prepare total RNA consisting of all the RNA present in retrovirus virions. You then set up an in vitro reaction with these components, and dNTPs (deoxynucleotide triphosphates) in an appropriate buffer for reverse transcription. Describe the nucleic acid product would you expect reverse transcriptase to produce in this situation. Would this system produce a double stranded DNA with duplicated LTRs? Explain why or why not. In poliovirus infected cells translation of cellular proteins from cellular mRNAs is blocked, while translation of viral proteins from viral mRNAs is efficient. What molecular mechanism is responsible for these observed effects? Explain.

Explanation / Answer

Polio virus is a positive stranded type of RNA virus. So, the genome of is is directly act as mRNA and immediately translated by the host cell. It dosnt require any initiation factor for translation. 5' end of polio virus RNA is very long - around 700 nucleotides and it is called as internal ribosome entry site which directs the translation of viral RNA. Polio virus mRNA is translated as one long polypeptide, which is cleaved into 10 viral proteins by proteases enzymes, which generate 10 folds of viral proteins.

In eukaryotcells, polio virus arrest or shutdown host protein synthesis. Translation in eukaryotes is initiated by mRNA 5' end cap structure which is formed by multiple subunits among it eIF4F component binds to mRNA to promote ribosome binding to mRNA for translation. Polio virus infection cleaves eIF4F (translation initiation factor) rendering this factor inactive for cap- dependent translation of host cell proteins.

Polio virus also activates translationalrepressors, which inhibit cap - dependent translation by binding to cap- binding subunit. Translation initiation factor binds to mRNA only when the translational repressor factor is phosphorylated. This phosphorylation and dephosphorylation if both factors is highly regulated in the cell.

In case of polio virus mRNA translationun affected, because of their protein production is independent of cap structure (independent of translation initiation factor).

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