Virology Final Part 3

Question 1

What is the structure of poliovirus?

Answer 1

• one piece of positive sense RNA
• naked, icosahedron
• capsid: 20 capsomeres made of 3 triangular subunits (each subunit is made of 3 proteins)

Question 2

How does poliovirus mature?

Answer 2

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

Question 3

Which subunit of the capsid is completely on the internal side of the capsid? What is the function of this subunit?

Answer 3

VP4; turns to the outside and forms part of the pore structure

Question 4

What is the function of VP1?

Answer 4

• 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

Question 5

What does the pore do?

Answer 5

Provides a channel for the RNA to pass through and go to the cytoplasm

Question 6

What is the structure of the polio genome?

Answer 6

VPg attached to the 5’ end, one ORF, and a polyA tail at 3’ end

Question 7

How is the polio genome translated?

Answer 7

Translated on a eukaryotic ribosome in the cytoplasm, makes a polyprotein of structural and non structural proteins

Question 8

How does polio initiate translation?

Answer 8

With the secondary structure IRES that can interact with the ribosome

Question 9

How does VPg get removed from the genome? When does it not get removed?

Answer 9

• It is cleaved by a cellular protease (exploited by the virus)
• if the new (+) RNAs are being used as a genome

Question 10

What protein associates with the 5’ cap in cap-dependent translation?

Answer 10

ElF-4G

Question 11

How does cap-independent translation differ from cap-dependent?

Answer 11

• 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

Question 12

What are the structural and non-structural genes that the genome encodes?

Answer 12

Structural: VP0, VP1, VP3

Non-structural: RDRP, VPg, proteases

Question 13

How does poliovirus eliminate competition for the ribosomes?

Answer 13

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)

Question 14

Why does poliovirus have RDRP encoded in the genome?

Answer 14

• 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

Question 15

What is unusual about polio’s genome in transcription?

Answer 15

• 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

Question 16

Does VPg play a role in translation of RNA?

Answer 16

No

Question 17

What is the role of the VPg?

Answer 17

A primer for transcription— needed to initiate genome replication, no function for assembly on a ribosome

Question 18

What is left behind when VPg gets cleaved?

Answer 18

Two uracils, which get translated into AA, so so that the next VPg can bind to it in transcription

Question 19

How many polio progenies can be made from one infected cell?

Answer 19

1000

Question 20

What would happen if you accidentally packaged a piece of (-) sense RNA?

Answer 20

RNA would not be able to cleave VP0, so the capsid would remain immature adn non infectious

Question 21

How do they attenuate poliovirus?

Answer 21

1. Grow culture in non-human cell line
2. Select the mutant viruses that are able to replicate
3. Propagate
4. Keep growing the polio viruses in the non-human cell line so it can get more mutations
5. The wild-type is diluted out of existence

Question 22

What are the features of the Sabin vaccine?

Answer 22

• OPV
• can replicate and mutate in feces and infect household members
• local immunity (IgA), maybe systemic immunity (IgG)
• attenuated virus

Question 23

What are the features of the Salk vaccine?

Answer 23

• IPV
• safe for immunocompromised people
• systemic immunity (IgG), could still infect gut (no IgA)
• inactivated virus

Question 24

How many serotypes are there for polio? How are they distinguished?

Answer 24

3; by antibodies

Question 25

What is VAPP?

Answer 25

Vaccine-associated paralytic polio, virus mutates and causes paralysis