Quiz 5

Question 1

Briefly explain how the 26S sgRNA is excluded during the assembly of Sindbis virus nucleocapsids.

Answer 1

because it lacks the origin of assembly sequence (OAS) that is recognized by the C protein to begin the nucleation process of nucleocapsid assembly

Question 2

What two host cell proteases are required to generate the mature envelope
spikes of Sindbis virus?

Answer 2

• signalase

- furin-like protease

Question 3

By what mechanism does virus release from infected cells occur for (i) a picornavirus; (ii) a togavirus?

Answer 3

i) lysis

ii) budding

Question 4

From what host species was influenza virus A/Hong Kong/1/68 (H3N2) isolated? Is this strain associated with propagated epidemics in humans?

Answer 4

Humans

-yes

Question 5

For Sindbis virus, what two models have been proposed to explain the process of uncoating?

Answer 5

• Membrane Fusion

- Injection

Question 6

What normal, cellular processes are required for togavirus (i) penetration, and (ii) uncoating?

Answer 6

i) Clathrin-Mediated Endocytosis (receptor mediated)

ii) acidification of the endosome causes conformational changes in virion

Question 7

Which of the Sindbis virus replication complexes derived from the non-structural polyprotein(s) can synthesize (i) both 49S (+)-ssRNA and 49S (-)-ssRNA; and (ii) both 49S (+)-ssRNA and 26S (+)-ssRNA?

Answer 7

i) nsP1 + P23 + nsP4

ii) ns P1+ nsP2 + nsP3 + nsP4

Question 8

Briefly outline the mechanism by which the P1234 polyprotein is produced during Sindbis virus early gene expression.

Answer 8

the opal termination sequence is read through

Question 9

What two genetic mechanisms have contributed to the evolution of rubella virus
and Sindbis virus since their divergence from a common ancestor?

Answer 9

• Recombination

- Mutation

Question 10

What is the function during the cellular infection cycle of the Sindbis virus 6K protein?

Answer 10

facilitates envelopement in virion assembly

Question 11

What is the predominant fate of genomic 49S RNA late in the Sindbis virus cellular infection cycle?

Answer 11

assembled into nucleocapsid and bud and produce new virus particles.

Question 12

Briefly explain how the hemagglutination inhibition (HI) assay could be used to identify an H5 subtype of influenza A virus.

Answer 12

If you have an unknown virus, change the reference antibody that you use. If you put it in your assay and it prevents hemmagluttination then it has the same type spike.

Question 13

What is the biochemical basis for the asymmetric accumulation of (+)- and (-)- strands that is observed for most kinds of ssRNA viruses?

Answer 13

• increase binding affinity on the one that you want.

Question 14

What are two possible mechanisms by which a (+)-ssRNA virus might express a protein encoded by an ORF that is far from the 5’-end of the genome? (hint: think about picornaviruses, as well as togaviruses).

Answer 14

• ribosome landing pad in the intergenic region. have two ribosome landing pads. One at 5’ end. One at 3’ end.
• togavirus - sgRNA to make a separate message

Question 15

What Sindbis virus RNA species are synthesized by the replication complex that contains the partially cleaved, non-structural polyprotein nsP1 + P23 + nsP4?

Answer 15

(+/-) 49S RNA

Question 16

What two mechanisms used for viral gene expression are common to both alphaviruses and rubiviruses?

Answer 16

• similar genome organization with two kinds of polyproteins. nonstructional translated from gRNA
• both sgRNA transcribed de novo

Question 17

Briefly outline the mechanism by which nsP4 is produced during Sindbis virus early gene expression.

Answer 17

• starts at P1234

- cleaved on the amino terminal by nsP2 to form P123 and nsP4

Question 18

Where do ribosomes bind to the viral genomic RNA during infection by (i) a togavirus, and (ii) a picornavirus?

Answer 18

• ribosomal 40S subunits bind to 5’ -cap, scan to AUG codon of ORF 1
• ribosomes bypass the 5’ end and bind directly to the ribosome landing pad (RLP)

Question 19

What event triggers the uncoating of Sindbis virus particles?

Answer 19

Endosome acidification which causes conformational change in virion

Question 20

Briefly outline the mechanism by which Sindbis virus particles are uncoated, and identify the differences between the two models that have been proposed for this process.

Answer 20

• direct injection - they don’t really touch. held separate by protein structure.
• membrane fusion - the two lipid bilayers fuse

Question 21

To what family and genus do influenza B virus belong?

Answer 21

Orthomyxoviridae

Question 22

type of viral protease

Answer 22

• c protease

- cleaves itself

Question 23

What viral protein is targeted by Tamiflu. What stage of the cellular infection cycle of influenza A virus is inhibited by Tamiflu?

Answer 23

• neuraminidase (NA spike protein)
• It takes off sialic acid from host and viral proteins. The action of the NA spike protein comes into play in release since the budding virions don’t want to attach to each other or the host cell.