Magor- Lecture 5: Polioviral replication Flashcards
Where does poliovirus replicate?
In the intestine
Poliovirus is fairly _________ and _________
contagious and deadly
for one person infected, they typically infect 3 others.
Baltimore classification
based on how many steps to mRNA
Poliovirus/rhinovirus start with a + RNA strand. Why do we call it + strand?
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
+ strand RNA viruses can synthesize their own ___________a and don’t need to package it with the RNA
polymerases
Why does a positive strand virus make negative strands?
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.
Poliovirus is a picornavirus because
it is one of the smallest viruses
Capsid is made up of how many copies of the four proteins? (VP1, VP2, VP3, VP4)
60 copies
Where are the four proteins (VP1, VP2, VP3, VP4) found on the capsid?
VP1, VP2, and VP3 are visible on the surface of the capsid
VP4 is inside making the capsid more firm
Reproductive life cycle of poliovirus
- 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.
- Once the RNA is in the cell, it’s already (+) strand, so it recruits ribosomes & ribosomes start synthesis of polyprotein. (translation)
- Polyprotein is made
- Polyprotein cleavage into bits
- RNA synthesis occurs on vesicle membranes
- (+) strand moves to vesicle
- (-) strand copies are made
- (+) strand copies are made. Some of them are brought back up for translation
- (+) strand copies translated
- Cleavage of the capsid precursors
- Assembly
- Exit by lysis
TRUE or FALSE
The cytopathic effect of poliovirus is huge
TRUE
An infected cell of the poliovirus are full of vacuoles or vesicles. Why is that?
those are all providing a place for the synthesis of those RNA strands on the outside of the vacuole.
Polyprotein on the first step folds back on itself and cleaves itself out. This is also called ____________.
autocleavage
RNA is translated into a single polypeptide.
It is cleaved by two virally encoded proteases ______ and _______
2Apro and 3Cpro
The structure of polioviral 3Dpol polymerase is an
- 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
How does the 3Dpol polymerase tell which is viral and host RNA?
- 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.
RNA secondary structure is determined by the __________
sequence
3AB
- 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
Within the 3AB protein, ______________ is found.
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.
RNA strand links to 3AB via ___________.
tyrosine
Every virus has to solve the end problem. How does the poliovirus do this?
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.
The primer starts synthesis on the ________ of 3AB
tyrosine
Protease 3C
Is gonna come along and cleaves the protein, releasing the VPg
VPg
Viral protein genome
- associated with the genome version of the virus, and that stays attached to that new strand.
Genomic RNAs can serve as _________ for the synthesis of new proteins.
mRNAs
In poliovirus, first step of translation is the __________
removal of VPg protein
What happens when capsid proteins are abundant?
RNA genomes are packaged
RNA recombination
- involves RNA polymerase template exchange
- mostly happens when it is making a negative strand, simply because there are way more positive strands around.
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?
It will switch to a different template and finish the strand.
Estimated ______ of viral templates recombine.
10-20%
Similarity of small pox and polio?
It is a virus that we could eradicate.
Inactivated vaccines
- 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.
Oral vaccine
- 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.
Difference of inactivated vaccines and oral vaccine in terms of inducing a memory response
Oral vaccine didn’t have to have a booster.
Inactivated vaccines need a booster to induce memory response.
What is the type of polio vaccine is currently used in Canada?
Inactivated Polio Vaccine (IPV)
The poliovirus causes paralysis that affects your thoracic region which means
you can’t breathe.
Iron lungs
What helped people with poliovirus breathe
How did they make an attenuated virus?
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.
Reversion mutant of the __________ strain made an infectious virus that caused polio.
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.
what is true about the vaccine-derived polio
It does not affect the vaccinated
In 2023, Polio cases in Africa linked to new oral vaccine
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.
