Quiz 5 Flashcards
Briefly explain how the 26S sgRNA is excluded during the assembly of Sindbis virus nucleocapsids.
because it lacks the origin of assembly sequence (OAS) that is recognized by the C protein to begin the nucleation process of nucleocapsid assembly
What two host cell proteases are required to generate the mature envelope
spikes of Sindbis virus?
- signalase
- furin-like protease
By what mechanism does virus release from infected cells occur for (i) a picornavirus; (ii) a togavirus?
i) lysis
ii) budding
From what host species was influenza virus A/Hong Kong/1/68 (H3N2) isolated? Is this strain associated with propagated epidemics in humans?
Humans
-yes
For Sindbis virus, what two models have been proposed to explain the process of uncoating?
- Membrane Fusion
- Injection
What normal, cellular processes are required for togavirus (i) penetration, and (ii) uncoating?
i) Clathrin-Mediated Endocytosis (receptor mediated)
ii) acidification of the endosome causes conformational changes in virion
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?
i) nsP1 + P23 + nsP4
ii) ns P1+ nsP2 + nsP3 + nsP4
Briefly outline the mechanism by which the P1234 polyprotein is produced during Sindbis virus early gene expression.
the opal termination sequence is read through
What two genetic mechanisms have contributed to the evolution of rubella virus
and Sindbis virus since their divergence from a common ancestor?
- Recombination
- Mutation
What is the function during the cellular infection cycle of the Sindbis virus 6K protein?
facilitates envelopement in virion assembly
What is the predominant fate of genomic 49S RNA late in the Sindbis virus cellular infection cycle?
assembled into nucleocapsid and bud and produce new virus particles.
Briefly explain how the hemagglutination inhibition (HI) assay could be used to identify an H5 subtype of influenza A virus.
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.
What is the biochemical basis for the asymmetric accumulation of (+)- and (-)- strands that is observed for most kinds of ssRNA viruses?
- increase binding affinity on the one that you want.
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).
- 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
What Sindbis virus RNA species are synthesized by the replication complex that contains the partially cleaved, non-structural polyprotein nsP1 + P23 + nsP4?
(+/-) 49S RNA
What two mechanisms used for viral gene expression are common to both alphaviruses and rubiviruses?
- similar genome organization with two kinds of polyproteins. nonstructional translated from gRNA
- both sgRNA transcribed de novo
Briefly outline the mechanism by which nsP4 is produced during Sindbis virus early gene expression.
- starts at P1234
- cleaved on the amino terminal by nsP2 to form P123 and nsP4
Where do ribosomes bind to the viral genomic RNA during infection by (i) a togavirus, and (ii) a picornavirus?
- 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)
What event triggers the uncoating of Sindbis virus particles?
Endosome acidification which causes conformational change in virion
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.
- direct injection - they don’t really touch. held separate by protein structure.
- membrane fusion - the two lipid bilayers fuse
To what family and genus do influenza B virus belong?
Orthomyxoviridae
type of viral protease
- c protease
- cleaves itself
What viral protein is targeted by Tamiflu. What stage of the cellular infection cycle of influenza A virus is inhibited by Tamiflu?
- 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.
