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Virology > Simple +ssRNA viruses: Picornaviridae and Flaviviridae > Flashcards

Simple +ssRNA viruses: Picornaviridae and Flaviviridae Flashcards

1
Q

What type of genome do simple +ssRNA viruses have?

A

monopartite

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2
Q

What are two examples of simple +ssRNA viruses

A

Picornaviridae

Flaviviridae

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3
Q

What viral family does poliovirus belong to

A

Picornaviridae

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4
Q

What viral family does Rhinoviruses belong to

A

Picornaviridae

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5
Q

What viral family does Enteroviruses belong to

A

Picornaviridae

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6
Q

What viral family does Hepatitis A virus belong to

A

Picornaviridae

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7
Q

What are medically important human viruses that are in the Picornaviridae family

A

Poliovirus
Rhinovirus
Enteroviruses
Hepatitis A virus

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8
Q

What are morphological features of Picornaviridae viruses

A

pico means small so they are small RNA viruses

7500bp genome

non-enveloped

icosahedral capsid

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9
Q

During gene expression do Picornaviruses have a 3’ poly A tail or a 5’ cap or both

A

Picornaviruses have a 3’ poly A tail

they do not have a 5’ cap, a viral protein VPg is attached to the 5’ end instead

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10
Q

Without a 5’ cap how do picornavirus viral proteins get translated

A

use an internal ribosomal entry site IRES

they have a viral protein VPg attached to the 5’ end as well

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11
Q

What is the IRES and how is it used in Picornaviruses

A

Internal Ribosome Entry Site

It is located in this order 5’ of start codon, IRES, 3’ Vp6 (end of genome)

adopts a specific 3D conformation that allows it to bind to ribosomes and direct translation

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12
Q

What is inhibited during picornavirus gene expression, what does this lead to

A

cap-dependent translation is inhibited of the host translation

target eIF4GI and 46II for degradation, these are necessary host translation factors

the degradation of the above host factors leads to only the translation of viral proteins so only viral proteins are made

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13
Q

How are the genes of picornaviruses expressed

A
  1. genome is translated as one polyprotein
  2. the polyprotein is then cleaved at specific sites by viral proteases, protease specific for picornaviruses is 3C
  3. the rate of cleavage is distinct at each site dictating how much of each protein is made
  4. structural proteins are made at the 5’ end and non-structural proteins are made at the 3’ end
  5. release non-structural proteins first and release structural proteins after
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14
Q

What end are structural proteins made in the picornaviruses

A

5’ end form structural proteins and these are released after the non-structural proteins

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15
Q

What end are non-structural proteins made in the picornaviruses

A

3’ end form the non-structural proteins and these are released first before the structural proteins are

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16
Q

What cleaves a polyprotein

A

proteases

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17
Q

Where does picornavirus replication occur

A

occurs on double membrane vesicles that are derived from the ER or autophagic membranes

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18
Q

Where are the double membrane vesicles where picornavirus replication occurs derived from

A

from the ER or autophagic membranes

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19
Q

What has to happen in picornaviruses before replication can begin

A

replication first requires translation of viral proteins

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20
Q

Are polymerase and other replicase proteins present in the virion of picornaviruses

A

no

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21
Q

What happens after translation of viral proteins in picornaviruses

A

the virus must make - RNA

dsRNA intermediate

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22
Q

Where does initiation occur in picornaviruses

A

initiation must occur at the 3’ end of the genome

23
Q

How is the genome held in picornavirus replication

A

genome is held in a circular form

24
Q

What is the process of picornavirus genome replication

A
  1. genome is held in a circular form
  2. Host Poly A and Poly C binding proteins are brought together by 3CD protein
  3. 3CD is the precursor for the polymerase, 3D is the polymerase
  4. once it is ready to leave it is activated by proteolytic cleavage and replicates RNA from the 3’ end of the template
25
Q

What is the role of Host Poly A and Poly C, viral 3DC and 3D in picornaviruses

A

picornavirus replication
genome is held in a circular form

Host Poly A and Poly C are binding proteins that are brought together by 3CD protein

3CD is the precursor of the polymerase

3D is the polymerase

once its ready to go, it is activated by the proteolytic cleavage and replicates RNA from the 3’ end of the template

26
Q

In picornavirus replication, once RNA synthesis initially begins what happens

A

Once RNA synthesis begins, the polymerase proceeds along the entire length of the template RNA

3’ end of the template will become available for further replication before the first complexes are finished

up to five complexes can be formed on a genome

this is called the replicative intermediate or RI

dsRNA is likely unwound by the viral helicase (maybe 2C protein)

27
Q

What is the replicative intermediate RI in picornaviruses

A

when the 3’ end of the template will become available for further replication before the first complexes are finished

up to five complexes can be formed on a genome

28
Q

What is dsRNA likely unwound by in picornaviruses

A

viral helicase maybe 2C

29
Q

How many complexes can be formed on a picornavirus genome

A

up to 5

replicative intermediates?

30
Q

In picornavirus after -RNA synthesis what occurs

A

+ RNA synthesis occurs in much the same way

31
Q

How does +RNA synthesis occur in picornaviruses

A

much the same way of -RNA synthesis

production of these RNA is asymmetric

much more + RNA is made than -RNA

only +RNA is release from replication complexes will be packaged into virions

32
Q

In picornaviruses is more +RNA or -RNA made

A

more +RNA is formed

33
Q

What type of RNA packaged into virions of the picornavirus

A

only +RNA is released from replication complexes and packaged into virions

34
Q

How does the picornavirus know which one to package

A

packaging signals is only on the +RNA strand and not on the -RNA strand, therefore only +RNA is packaged into virions

35
Q

What are medically relevant Flaviviridae

A

arboviruses

West Nile Virus
Zika Virus
Dengue Virus
along with many others

36
Q

What are morphological features of the Flaviviridae family

A

+ssRNA

enveloped

virion is spherical

50um in diameter

37
Q

What are the similarities between Flaviviridae and Picornaviridae gene expression, two main points

A

gene expression is very similar

genome is translated into a single polyprotein and cleaved by viral proteases

structural proteins at 5’ and nonstructural proteins at 3’ end

38
Q

What are the differences between Flaviviridae and Picornaviridae gene expression

A

Flaviviridae have

have a 5’ cap

do not have a poly A tail

sfRNA: subgenomic flavirus RNA

39
Q

What are sfRNA and what viral family are they located in

A

subgenomic flavirus RNA

found in Flaviviridae

40
Q

Is sfRNA transcribed

A

it is not transcribed

41
Q

How is sfRNA formed

A

it is NOT transcribed

it is the incomplete digestion of gRNA by cellular exoribonucleases

42
Q

What is the function of sfRNA

A

has important functions countering IFN, RNAi, RNA decay and transmission

43
Q

Where does Flavivirus replication occur

A

viral replication occurs on the ER-derived membranes that form viral factories

these are single membranes

44
Q

What are the four viral proteins that are NOT transmembrane proteins in Flaviviridae

A

polymerase NS5
protease NS3
capsid protein
NS1

45
Q

What is the role of NS5, NS3, capsid protein and NS1 in Flaviviridae and where are they located

A

not transmembrane

NS5: polymerase, needs to move so it cannot be embedded in the membrane

NS3: protease, has to cleave so it cannot be embedded in the membrane

capsid protein: capsid cannot be embedded in the membrane

NS1

46
Q

Does it matter which side of the membrane the polymerase is on in Flaviviridae replication

A

yes, the membrane is not a straight line, its in some type of vesicle form, the RNA has to be exposed for translation at some point so the non-transmembrane protein have to be on the outside of the membrane and not transmembrane to help in this process

47
Q

The genome of Flaviviridae and Picornaviridae both encode for what?

A

a polyprotein that is cleaved by viral proteases

48
Q

When are replicative intermediates formed

A

during replication where multiple initiations occur, up to 5 complexes can be formed in the Picornaviridae

49
Q

What does it mean by RNA replication is asymmetric

A

means that much more +RNA is produced that -RNA

50
Q

Does the IRES allow for transcription, replication, or translation

A

translation

51
Q

How do Picornaviruses prevent host translation

A

cap-dependent translation is inhibited —- host translation has 5’ cap
the virus targets the eIF4G and 46II for degradation (these are necessary host translational factors)
host translation is prevented so only viral proteins are made

52
Q

How is the picornavirus polymerase activated

A

activated by proteolytic cleavage and replicates RNA from the 3’ end of the template

53
Q

What does it mean if RNA virus replication is asymmetric

A

if RNA virus replication is asymmetric then much more + or - sense RNA is made over the other
if there was equal amounts then they would form together making dsRNA that would be recognized by the host

in picornavirus replication more + RNA is made than - RNA

54
Q

Why do PV replicate asymmetrically

A

if RNA virus replication is asymmetric then much more + or - sense RNA is made over the other
if there was equal amounts then they would form together making dsRNA that would be recognized by the host

in picornavirus replication more + RNA is made than - RNA

Virology (6 decks)

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