gene therapy, viral oncotherapy, and to deliver vaccines to prevent infectious diseases. How ironic it is that our study of the viruses that cause disease has led to their transformation into therapeutic agents!
REFERENCES
Review Articles
Baltimore D. 1971. Expression of animal virus genomes. Bacteriol Rev 35:235–241.
Knott GJ, Doudna JA. 2018. CRISPR-Cas guides the future of genetic engineering. Science 361:866–869.
Krupovic M, Dolja VV, Koonin EV. 2019. Origin of viruses: primordial replicators recruiting capsids from hosts. Nat Rev Microbiol 17:449–458.
Papers of Special Interest
Fiers W, Contreras R, Duerinck F, Haegeman G, Iserentant D, Merregaert J, Min Jou W, Molemans F, Raeymaekers A, Van den Berghe A, Volckaert G, Ysebaert M. 1976. Complete nucleotide sequence of bacteriophage MS2 RNA: primary and secondary structure of the replicase gene. Nature 260:500–507.
The first complete genome sequence of any kind.
Taniguchi T, Palmieri M, Weissmann C. 1978. QB DNA-containing hybrid plasmids giving rise to QB phage formation in the bacterial host. Nature 274:223–228.
The first infectious virus from a cloned DNA copy of a viral genome.
Crotty S, Cameron CE, Andino R. 2001. RNA virus error catastrophe: direct molecular test by using ribavirin. Proc Natl Acad Sci U S A 98:6895– 6900.
Only a two-fold increase in poliovirus genome mutations is needed to push the population over the error threshold.
Elbashir SM, Harborth J, Lendeckel W, Yalcin A, Weber K, Tuschl T. 2001. Duplexes of 21-nucleotide RNAs mediate RNA interference in cultured mammalian cells. Nature 411:494–498.
The first report that synthetic siRNAs can silence gene expression in mammalian cells.
Jinek M, Chylinski K, Fonfara I, Hauer M, Doudna JA, Charpentier E. 2012. A programmable dual-RNA-guided DNA endonuclease in adaptive bacterial immunity. Science 337:816–821.
The Cas9 endonuclease is engineered into a two-component system by fusing the two RNA molecules into a single-guide RNA that, when combined with Cas9, cuts the DNA target specified by the guide RNA.
Wolf YI, Kazlauskas D, Iranzo J, Lucía-Sanz A, Kuhn JH, Krupovic M, Dolja VV, Koonin EV. 2018. Origins and evolution of the global RNA virome. mBio 9:e02329–18.
Analysis of RdRp sequences illuminates RNA virus evolution.
STUDY QUESTIONS
1 The Baltimore scheme is useful for predicting the path from the viral genome to mRNA, but to do this a few other facts are needed. Which of the following is not one of these facts?mRNA cannot be made from ssDNAdsRNA can be directly translated into protein since it contains a (+) strandA gapped dsDNA must be repaired before transcription can beginCells do not produce RNA-dependent RNA polymeraseNone of these are incorrect
2 Why is mRNA placed at the center of the Baltimore scheme?Because all virus particles contain mRNAThere is no specific reasonBecause all viral genomes are mRNAsBecause mRNA must be made from all viral genomesBecause Baltimore studied mRNA
3 Which DNA genome, on entry into the cell, can be immediately copied into mRNA?dsDNAGapped dsDNACircular ssDNALinear ssDNAAll of the above
4 Which statement about viral RNA genomes is correct?(+) ssRNA genomes may be translated to make viral proteindsRNA genomes can be directly translated to make viral protein(+) ssRNA virus replication cycles do not require a (–) strand intermediateRNA genomes can be copied by host cell RNA-dependent RNA polymerasesAll of the above
5 Will viral RNA extracted from virus particles of a virus with a (–) ssRNA genome initiate an infection after transfection into a permissive cell? Into a susceptible cell? Explain your answers.
6 Why must all RNA virus genomes encode an RNA-dependent RNA polymerase?
7 Viruses with segmented RNA genomes can undergo a process that viruses with unimolecular RNA genomes cannot. What is this process called and how does it occur?
8 This is the genome of a (–) strand RNA virus. It is 14 kb in length.If this purified RNA is introduced into cultured cells by transfection, will infectious viruses be produced? Why or why not?Describe two different strategies for producing seven different viral polypeptides from this genome.
9 You infect two plates of cells with virus at multiplicities of infection (MOI) of 1 and 10. After 4 h of incubation, about two-thirds of the cells are dead on the plate with an MOI of 1, and all cells are dead on the plate with an MOI of 10. Explain these observations.
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