Magor- Lecture 5: Polioviral replication

Question 1

Where does poliovirus replicate?

Answer 1

In the intestine

Question 2

Poliovirus is fairly _________ and _________

Answer 2

contagious and deadly

for one person infected, they typically infect 3 others.

Question 3

Baltimore classification

Answer 3

based on how many steps to mRNA

Question 4

Poliovirus/rhinovirus start with a + RNA strand. Why do we call it + strand?

Answer 4

Because it is already in the orientation in order to be translated.

It is already in the orientation that it needs to make the proteins that it needs

Question 5

+ strand RNA viruses can synthesize their own ___________a and don’t need to package it with the RNA

Answer 5

polymerases

Question 6

Why does a positive strand virus make negative strands?

Answer 6

RNA synthesis requires a template in the same way as DNA synthesis requires a template.

You make that (-) strand so that you have a template to make the (+) strand.

Question 7

Poliovirus is a picornavirus because

Answer 7

it is one of the smallest viruses

Question 8

Capsid is made up of how many copies of the four proteins? (VP1, VP2, VP3, VP4)

Answer 8

60 copies

Question 9

Where are the four proteins (VP1, VP2, VP3, VP4) found on the capsid?

Answer 9

VP1, VP2, and VP3 are visible on the surface of the capsid
VP4 is inside making the capsid more firm

Question 10

Reproductive life cycle of poliovirus

Answer 10

1. Poliovirus binds to PVR. This is an active step and it causes a conformational change in the capsid protein VP1 to get into the membrane in order to get RNA into the cell.
2. Once the RNA is in the cell, it’s already (+) strand, so it recruits ribosomes & ribosomes start synthesis of polyprotein. (translation)
3. Polyprotein is made
4. Polyprotein cleavage into bits
5. RNA synthesis occurs on vesicle membranes
6. (+) strand moves to vesicle
7. (-) strand copies are made
8. (+) strand copies are made. Some of them are brought back up for translation
9. (+) strand copies translated
10. Cleavage of the capsid precursors
11. Assembly
12. Exit by lysis

Question 11

TRUE or FALSE

The cytopathic effect of poliovirus is huge

Answer 11

TRUE

Question 12

An infected cell of the poliovirus are full of vacuoles or vesicles. Why is that?

Answer 12

those are all providing a place for the synthesis of those RNA strands on the outside of the vacuole.

Question 13

Polyprotein on the first step folds back on itself and cleaves itself out. This is also called ____________.

Answer 13

autocleavage

Question 14

RNA is translated into a single polypeptide.
It is cleaved by two virally encoded proteases ______ and _______

Answer 14

2Apro and 3Cpro

Question 15

The structure of polioviral 3Dpol polymerase is an

Answer 15

• RNA dependent RNA polymerase.
  It needs RNA template in order to make RNA & then it polymerizes RNA form that RNA template.
• unique to virus
• specific for RNA template
• error-prone = doesn’t have exonuclease activity, doesn’t go back & correct mistakes
• “quasi-species” = no WT virus

higher error rate=small virus

Question 16

How does the 3Dpol polymerase tell which is viral and host RNA?

Answer 16

• RNA virus has a very specific structure of hairpins that the polymerase is looking for
• The host RNA is just gonna have that structure.
• The 3D structure is totally dependent on the base-pairing that happens within the strand.

Question 17

RNA secondary structure is determined by the __________

Answer 17

sequence

Question 18

3AB

Answer 18

• VPg precursor
• brings template RNA over to the surface of the vacuole
• has a hydrophobic little part that inserts into the membrane & that’s how it holds this whole process on the outside of those vacuoles.
• takes RNA to the membrane

Question 19

Within the 3AB protein, ______________ is found.

Answer 19

Tyrosine with a hydroxyl group

The hydroxyl group is being used as the primer to help the poliovirus copy all the way to the end.

Question 20

RNA strand links to 3AB via ___________.

Answer 20

tyrosine

Question 21

Every virus has to solve the end problem. How does the poliovirus do this?

Answer 21

It uses the 3AB protein as the site where this incoming base (which is a uracil) will actually do the nucleophilic attack and form a covalent bond between this triphosphate & hydroxyl group.

Question 22

The primer starts synthesis on the ________ of 3AB

Answer 22

tyrosine

Question 23

Protease 3C

Answer 23

Is gonna come along and cleaves the protein, releasing the VPg

Question 24

VPg

Answer 24

Viral protein genome

• associated with the genome version of the virus, and that stays attached to that new strand.

Question 25

Genomic RNAs can serve as _________ for the synthesis of new proteins.

Answer 25

mRNAs

Question 26

In poliovirus, first step of translation is the __________

Answer 26

removal of VPg protein

Question 27

What happens when capsid proteins are abundant?

Answer 27

RNA genomes are packaged

Question 28

RNA recombination

Answer 28

• involves RNA polymerase template exchange
• mostly happens when it is making a negative strand, simply because there are way more positive strands around.

Question 29

IN RNA recombination, what happens if it is synthesizing a copy of itself and it runs into errors that just doesn’t look right to that polymerase?

Answer 29

It will switch to a different template and finish the strand.

Question 30

Estimated ______ of viral templates recombine.

Answer 30

10-20%

Question 31

Similarity of small pox and polio?

Answer 31

It is a virus that we could eradicate.

Question 32

Inactivated vaccines

Answer 32

• protein vaccine
• the virus is either heat-killed or chemically inactivated
• you have to keep the protein cold
• reduced the incidence of poliovirus almost immediately
• induce antibody response, rarely induce cellular immunity.

Question 33

Oral vaccine

Answer 33

• better than inactivated vaccines because it is a live attenuated virus.
• it is synthesizing new virions and viral proteins that are targets of both humoral and cellular immune responses.
• elicits a much better immune response than inactivated vaccine
• didn’t have to stay cold; administer by just dropping into children’s mouth.

Question 34

Difference of inactivated vaccines and oral vaccine in terms of inducing a memory response

Answer 34

Oral vaccine didn’t have to have a booster.
Inactivated vaccines need a booster to induce memory response.

Question 35

What is the type of polio vaccine is currently used in Canada?

Answer 35

Inactivated Polio Vaccine (IPV)

Question 36

The poliovirus causes paralysis that affects your thoracic region which means

Answer 36

you can’t breathe.

Question 37

Iron lungs

Answer 37

What helped people with poliovirus breathe

Question 38

How did they make an attenuated virus?

Answer 38

You grow it in non-human cells & hope that it changes to adapt to those cells and then it is different enough when it goes back in to humans that it’s not paralytic.

Question 39

Reversion mutant of the __________ strain made an infectious virus that caused polio.

Answer 39

P3 Sabin vaccine

The virus mutates all the time and can reform infectious virus that can cause paralysis, although that doesn’t happen in the vaccinated people.

Although the amino acid changes did not re-make the original virus-the new proteins could assemble a functional capsid and be infectious.

Question 40

what is true about the vaccine-derived polio

Answer 40

It does not affect the vaccinated

Question 41

In 2023, Polio cases in Africa linked to new oral vaccine

Answer 41

Improved vaccine is not reaching enough children

They engineered changes to the 5’ end of the virus limiting mutations, and decreasing its ability to recombine.

However, unvaccinated people are at risk in the rare case of viral reversion.