Читать книгу Principles of Virology - Jane Flint, S. Jane Flint - Страница 299

1 Which of the following statements concerning viral RNA synthesis is incorrect?The RNA genome must be copied end to endmRNAs must be produced that can be translated by the cellRNA polymerases were first identified by labeling cells with radioactive precursorsA positive-strand viral RNA must enter the cell together with an RNA polymeraseA viral RNA polymerase copies the viral RNA genome

2 Consider a virus with a (+) strand RNA genome 8 kb in length, which encodes eight proteins. Which of the following is a known mechanism for producing all eight proteins from this genome?A single polyprotein is synthesized, which is then processed by proteases to form eight proteinsThe RNA is cleaved into eight fragments, each of which is translated into a different proteinImmediately upon entering the cells, the viral RNA polymerase that is carried into the cell within the virus particle produces eight subgenomic mRNAs from the (+) strand RNA genomeThere is no way to produce multiple proteins from a eukaryotic RNA

3 Which situation best illustrates the finding that for some viruses, the nucleic acid does not leave the particle?Cap snatching during the production of influenza viral mRNAsPolyadenylation by slippage of RNA polymerase at intergenic sequences on the templateSynthesis of reovirus mRNAsVPg priming of polioviral RNA synthesis

4 Virus particles of (–) strand RNA viruses contain an RNA-dependent RNA polymerase. Virus particles of (+) strand RNA viruses (except retroviruses) do not contain an RNA-dependent RNA polymerase. As cells do not have RNA-dependent RNA polymerase, where does the RNA polymerase of (+) strand RNA viruses come from?

5 You purify all the influenza virus mRNAs from an infected cell. When you transfect these influenza viral mRNAs into a permissive cell, no infectious virus is produced. Why are the influenza viral mRNAs not infectious?

6 Before genome sequencing was possible, UV light was used to determine the sizes of vesicular stomatitis virus (VSV) mRNAs. In this experiment, viral particles are irradiated, and then mRNA synthesis is allowed to proceed. When UV light produces a lesion in the genome RNA, mRNA synthesis stops. Because of this property, synthesis of long mRNAs is more sensitive to UV light, while synthesis of short mRNAs is more resistant to UV light. The following UV sensitivity map was obtained:Use your knowledge of how VSV mRNAs are produced to explain this UV sensitivity map.

7 Influenza virus mRNAs are shorter than the genomic RNAs from which they are made. What is the mechanism for production of full-length copies of the genomic (–) strand RNAs for incorporation into newly synthesized virus particles?

8 Some RdRPs require a primer to initiate RNA synthesis. What are two different types of primer used for RNA synthesis?

9 The palm domain of poliovirus RdRP contains a GDD motif. Explain why changing D (Asp) to alanine produces an inactive polymerase that can no longer copy RNA templates.