1B. Which protein complex is doing the process shown in “A”? 1C.Why can this hap

Question

1B. Which protein complex is doing the process shown in “A”?

1C.Why can this happen as soon as the genome enters the cell?

2. Over on the upper right side of the figure, labeled “B”, why does the virus shut off host cell translation and transcription? What is the benefit of this to the virus?

3. What viral process is happening part C and what enzyme does this?

4. What are the blue lines made in part D and what is the dual purpose of these blue lines?

Pro-apoptotic Anti-apoptotic Shut off host cell Sta 0 host cell (cap Polyprotein Interactions between the vius and the cel cycle ral replication complex dsRNA (atency?) strand (goniome 3 3 3 Cell lysis Veal ogrees Nature Reviews Microbiology 3, 765-776 (October 2005) I dol:10.1038/nrmicro1284

Explanation / Answer

1A. After entry IRES mediated translation occurs at first. An internal ribosome entry site (IRES) is a RNA element, located in the 5'UTR of RNA viruses that allows for translation initiation in an cap-independent manner.

1B. In the case of most picornaviruses, this IRES mediaed translation is accomplished by viral proteolytic cleavage of eIF4G so that it cannot interact with the 5'cap binding protein eIF4E. Interaction between these two eukaryotic initiation factors (eIFs) of the eIF4F complex is necessary for 40S ribosomal subunit recruitment to the 5' end of mRNAs. The virus may even use partially-cleaved eIF4G to aid in initiation of IRES-mediated translation. Many viral IRES (and cellular IRES) require additional proteins to mediate their function, known as IRES trans-acting factors (ITAFs).

1C. The primary translation product of the picornavirus genome is a single large protein, named a polyprotein, which is processed to the mature viral polypeptides by progressive, co- and post-translational cleavages. Replication of the picornaviruses is thus entirely dependent upon the proteolysis of viral precursor proteins or polyprotein.

2. Viruses have evolved ways of interacting with the host translational machinery to shutoff host gene expression. This global inhibition of cellular protein synthesis serves to ensure maximal viral gene expression and to evade host immune response.
All the viruses inducing the shutoff of translation are able to continue to translate at least part of their mRNAs using non-canonical translation such as IRES.

3. Viral single stranded RNA replication occurs.

The polyprotein which is produced by IRES mediated translation in first step cuts itself at specific sites by internal protease action. One of the products of this protease action is a viral RNA polymerase, which can use viral ssRNA as template for making a complementary RNA strand. Thus, RNA polymerase helps this replication.

4. The blue lines made in part D are newly synthesized lots of copies of viral single stranded RNA in the cytoplasm.

The dual purpose of these blue lines are -

i) These RNAs can then be translated just as the first one was, and so lots of viral polyprotein starts getting made.

ii) New genomic RNA is believed to be packaged into preassembled procapsids.

Related Questions

Navigate

• Browse (All)
• Browse 1
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.