Deck 13: Togaviruses

Question 1

Which of the following members of the Togavirus family caused an epidemic in the Indian Ocean region in 2005?

A) Ross River virus
B) Sindbis virus
C) Venezuelan encephalitis virus
D) Chikungunya virus
E) Rubella virus

Answer 1

D

Question 2

Which of the following describes the mechanism used by togaviruses to switch from synthesizing negative-strand genomes to making positive-strange genomes?

A) Phosophorylation of the polymerase protein.
B) Dephosphorylation of the polymerase protein.
C) Glycosylation of the polymerase protein.
D) Methylation of the polymerase protein.
E) Proteolytic cleavage of the polymerase protein.

Answer 2

E

Question 3

Infection of vertebrate cells with a togavirus does not cause cytopathic effects but leads to a persistent infection instead.

Answer 3

False

Question 4

How are the structural proteins in togaviruses expressed?

A) They are translated from the negative-sense strands after genome replication.
B) They are translated directly from incoming genomes.
C) They are translated from a subgenomic RNA.
D) They are only translated from newly synthesized full-length genomes.
E) None of the above are correct.

Question 5

What is the definition of a "dead-end" host for an arbovirus?

A) A vertebrate host that does not transmit the virus efficiently.
B) An insect vector that dies before it can transmit the virus.
C) A vertebrate host that does not get sick when infected with the virus.
D) An insect vector that poorly replicates the virus.
E) A virus that can not replicate in the lungs of the host

Question 6

The open reading frame that takes up the 5' end of the togavirus genome encodes which of the following?

A) The nonstructural proteins.
B) The capsid proteins.
C) The IRES sequence.
D) The envelope proteins.
E) The proteins that shut down host defenses.

Question 7

Which of the following describes an interesting feature of the envelope of a togavirus?

A) There are 240 copies of the envelope protein in the envelope.
B) The envelope proteins are arranged with icosahedral symmetry.
C) The envelope is composed of a lipid bilayer.
D) The envelope is inside the capsid.
E) The envelope only contains one type of protein.

Question 8

Which of the following describes the mechanism used to regulate the various functions of the RNA-dependent RNA polymerase from togaviruses?

A) Proteolytic cleaveage.
B) Post-translational phosphorylation.
C) Post-translational glycosylation.
D) Interaction with viral cofactors.
E) Interaction with viral structural proteins.

Question 9

How does a togavirus ensure that only full length genomes are packaged into the virions?

A) Only full length genomes will fit into the capsid.
B) Only full length genomes are produced near the site of assembly.
C) Only full length genomes can bind to the envelope glycoproteins.
D) Only full length genomes contain the packaging signal.
E) Only full length genomes can be processed by the viral nuclease.

Question 10

Which of the following members of the togavirus family is not transmitted via mosquitoes?

A) Sindbis virus
B) Equine Encephalitis virus
C) Rubella virus
D) Ross River virus
E) Semliki Forest virus

Question 11

Which of the following allows the production of the P1234 nonstructural protein in a togavirus?

A) Ribosomal frameshifting.
B) Production of the subgenomic mRNA.
C) Proteolytic cleavage.
D) Readthrough of a stop codon.
E) Initiation of translation at a downstream start codon.

Question 12

Most arthropod-borne viruses can replicate in both insect cells and mammalian cells.

Question 13

During infection with a togavirus, the subgenomic mRNAs represent the complementary strand of which of the following?

A) The full-length positive-strand genome.
B) The 3' half of the positive-strand genome.
C) The 3' half of the negative-strand antigenome.
D) The 5' half of the positive-strand genome.
E) The 5' half of the negative-strand antigenome.

Question 14

Which of the following components of the togavirus virion bind to the host cell receptor?

A) Lipid envelope
B) Capsid protein
C) HA protein
D) E1 glycoprotein
E) E2 glycoprotein

Question 15

During entry of a togavirus virion, which of the following events may help disrupt the nucleocapsids and release the genomic RNA into the host cell?

A) Uptake of the virion into the endosome.
B) The increase in pH inside the endosome.
C) Degradation of the capsid proteins by the viral protease.
D) Binding of the ribosomes to the genomic RNA.
E) Binding of viral polymerase to the genomic RNA.

Question 16

If you add togavirus virions to host cells and then lower the pH of the medium, what will happen?

A) The virions will become inactivated.
B) The virus will bind more tightly to the host cell receptor.
C) The virions will fuse to the plasma membrane of the cell.
D) The virus will be released from the host cell receptor.
E) The virions will be taken up by receptor mediated endocytosis.

Question 17

In an experiment, mutation of bases at the very 5' end of the togavirus genome reduces the amount of the negative-strand of the genome produced.What does this result suggest?

A) That the virus genome contains an IRES sequence.
B) That the packaging sequence is only found at the 5' end of the genome.
C) That the replication complex binds to both ends of the genome.
D) That the genome forms a covalently closed circle for replication.
E) That a protein is used as a primer for genome replication.

Question 18

An experiment was done in togaviruses where the nsP2 protein was mutated so that it can proteolytically cleave the P123 protein very quickly.Which of the following describes the results of this experiment?

A) Inability of the virus to produce negative-strand genomes.
B) Inability of the virus to produce positive-strange genomes.
C) Inability of the virus to produce subgenomic mRNAs.
D) Faster replication of the virus genome.
E) Production of higher levels of virus particles.

Question 19

Which of the following is the correct description for the term arboviruses?

A) Viruses that are all in the togavirus family.
B) Viruses that all have an RNA genome.
C) Viruses that are all capable of infecting the liver.
D) Viruses that can all cause diseases in humans.
E) Viruses that all use an insect as a transmission vector.

Question 20

Translation of the subgenomic mRNA from togaviruses occurs on ribosomes that are located on or in which of the following cellular compartments?

A) Mitochondria
B) Nucleus
C) Cytoplasm
D) Trans-Golgi vesicle
E) Endoplasmic reticulum

Question 21

The subgenomic mRNA from togaviruses is synthesized from a subgenomic negative-strand RNA.

Question 22

Alphaviruses, which are members of the togavirus family, have been developed as useful vectors for the expression of proteins in various human and insect cells.Describe two situations where alphaviruses could be used as vectors in biology or medicine.

Question 23

One of the advantages of the alphavirus vector that uses a double subgenomic RNA for expressing foreign proteins is that it does NOT need a helper virus to produce virions.

Question 24

The production of the subgenomic mRNA allows togaviruses to synthesize 10 times more structural proteins than non-structural proteins.

Question 25

The P123 version of the polymerase protein from togaviruses can autocatalytically cleave itself into the individual nonstructural proteins.

Question 26

The togaviruses have their non-structural protein coding sequences at the 5' end of the viral genome while the picornaviruses and the flaviviruses have the non-structural protein coding sequences at the 5' end.Explain how this difference is important in the replication cycle of the togaviruses.

Question 27

There are two proposed mechanisms for how togaviruses assemble their virions.Describe the two mechanisms and any available evidence that supports them.