Virology Final Part 3 Flashcards
What is the structure of poliovirus?
- one piece of positive sense RNA
- naked, icosahedron
- capsid: 20 capsomeres made of 3 triangular subunits (each subunit is made of 3 proteins)
How does poliovirus mature?
Immature form: VP0, VP1, VP3
Maturation: RNA genome is inserted and acts like a ribozyme; VP0 cleaves into VP2 and VP4
Mature: VP1, VP2, VP3, VP4
Which subunit of the capsid is completely on the internal side of the capsid? What is the function of this subunit?
VP4; turns to the outside and forms part of the pore structure
What is the function of VP1?
- Virus’ anti-receptor, forms a canyon that interacts with CD155
- induces conformational changes in the capsid, and N terminal end of the VP1 protein inserts into the cell to form a pore
What does the pore do?
Provides a channel for the RNA to pass through and go to the cytoplasm
What is the structure of the polio genome?
VPg attached to the 5’ end, one ORF, and a polyA tail at 3’ end
How is the polio genome translated?
Translated on a eukaryotic ribosome in the cytoplasm, makes a polyprotein of structural and non structural proteins
How does polio initiate translation?
With the secondary structure IRES that can interact with the ribosome
How does VPg get removed from the genome? When does it not get removed?
- It is cleaved by a cellular protease (exploited by the virus)
- if the new (+) RNAs are being used as a genome
What protein associates with the 5’ cap in cap-dependent translation?
ElF-4G
How does cap-independent translation differ from cap-dependent?
- initiation begins directly on AUG, on the IRES
- ITAF: IRES trans-acting factors— host proteins that are exploited by polio to mediate translation
- once translation is initiated it is the same
What are the structural and non-structural genes that the genome encodes?
Structural: VP0, VP1, VP3
Non-structural: RDRP, VPg, proteases
How does poliovirus eliminate competition for the ribosomes?
It has a protease that damages the part of the cap-binding complex (elF4G)that cellular mRNA needs to assemble onto ribosomes (only AFTER the first translation, because the protease needs to be translated)
Why does poliovirus have RDRP encoded in the genome?
- the cell lacks a polymerase that can read RNA as a template and synthesize genome RNA and mRNA
- genome is replicated in the cytoplasm and the host cell enzyme is in the nucleus
What is unusual about polio’s genome in transcription?
- it uses a modified VPg as the primer (provides the 3’ OH group for the addition of the next nucleotide)
- VPg is modified by adding 2 uracil nucleotides and OH
Does VPg play a role in translation of RNA?
No
What is the role of the VPg?
A primer for transcription— needed to initiate genome replication, no function for assembly on a ribosome
What is left behind when VPg gets cleaved?
Two uracils, which get translated into AA, so so that the next VPg can bind to it in transcription
How many polio progenies can be made from one infected cell?
1000
What would happen if you accidentally packaged a piece of (-) sense RNA?
RNA would not be able to cleave VP0, so the capsid would remain immature adn non infectious
How do they attenuate poliovirus?
- Grow culture in non-human cell line
- Select the mutant viruses that are able to replicate
- Propagate
- Keep growing the polio viruses in the non-human cell line so it can get more mutations
- The wild-type is diluted out of existence
What are the features of the Sabin vaccine?
- OPV
- can replicate and mutate in feces and infect household members
- local immunity (IgA), maybe systemic immunity (IgG)
- attenuated virus
What are the features of the Salk vaccine?
- IPV
- safe for immunocompromised people
- systemic immunity (IgG), could still infect gut (no IgA)
- inactivated virus
How many serotypes are there for polio? How are they distinguished?
3; by antibodies
What is VAPP?
Vaccine-associated paralytic polio, virus mutates and causes paralysis
