Chapter 14: Picornaviruses and other (+) RNA

Question 1

Poliovirus Capsid

Answer 1

30 nm in diameter
Icosahedral
60 identical subunits (protomers)
Canyon- contain anti-receptor

Question 2

Each Protomer has 4 different proteins

Answer 2

VP1, VP2, VP3 at surface

VP4 buried beneath shell

Question 3

Canyon

Answer 3

Surface depression

Question 4

Poliovirus Genome

Answer 4

7.7 kb, (+) ssRNA-> act as mRNA upon infection

6 features

Question 5

Genome Feature 1

Answer 5

No cap - so ribosome does not bind to 5’ end

Question 6

Genome Feature 2

Answer 6

Viral Protein Genome linked covalently linked to 5’ end
2 functions:
“Primer” for both (+) and (-) RNA synthesis
“Packaging signal”: only RNA lnked to VPg will be packaged

Question 7

Genome Feature 3

Answer 7

5’ UTR: untranslated region, long (743 nt) leader sequence
Contains Internal Ribosome Entry Site
Important for translation and virulence

Question 8

Genome Feature 4

Answer 8

Single ORF: Encode a single “polyprotein”
All structural genes except VPg gene on left side of genome
non-structural genes plus VPg on right side of genome

Question 9

Genome Feature 5

Answer 9

3' UTR: 50-100nt
Important in (-) strand synthesis

Question 10

Genome Feature 6

Answer 10

Poly A at 3’ end

Question 11

Poliovirus Anti-receptor

Answer 11

Capsid proteins in canyon
Not surface protrusion
Hide from immune surveillance (canyon is too narrow for antibody to access)

Question 12

Poliovirus Receptor

Answer 12

Glycoprotein CD 155 (immunoglobulin-like), on many cell types
Major conformational change -> lost VP4

Question 13

Poliovirus Entry and Uncoating

Answer 13

Endocytosis
VPg-RNA released into cytoplasm
VPg removed by cell enzyme

Question 14

Poliovirus Translation and post-translational modification

Answer 14

Ribosome binds IRES and moves to AUG
Initiation complex forms
Genome -> a polyprotein->autoproteolytical cleavage by viral proteases

Question 15

Polyproteins

Answer 15

P1-> myristylated-> all capsid proteins

P2. P3 -> VPg, non-structural proteins

Question 16

Transcription and Genome Replication

Answer 16

After translation
Occur on replication complex
Viral RdRp as the 1st nt onto VPg
Replicative intermediate

Question 17

(+) RNA has 3 functions

Answer 17

mRNA for translation
Template fo (-)RNA synthesis
Genome for packaging

Question 18

Poliovirus Assembly

Answer 18

P1->VP0, VP3, VP1->1 promoter-> 1 pentamer -> procapsid

VPg-RNA inserted

Question 19

Maturation

Answer 19

VP0 cleaved -> VP2 + VP4

Total virion proteins = 4x5x12+1(VPg)

Question 20

Poliovirus Exit

Answer 20

via cell lysis
Burst size: 10^5 virions/infected cell
Cytopathic effects

Question 21

1 “re-program” events

Answer 21

inhibit host gene expression

Question 22

Viral protease shutoff host translation

Answer 22

Protease 2A cleave cap-binding protein
Ribosome no longer recognize capped mRNA
No cellular mRNA translation
Viral translation still occurs

Question 23

Viral proteins block vesicle traffic from ER to cis Golgi

Answer 23

Proteins 2B and 3A inhibit host protein secretion

More vesicles available for viral RNA replication on vesicle

Question 24

Cytopathology and polio (poliomyelitis)

Answer 24

fecal-oral transmission
Receptors only in human nasopharynx, gut, spinal cord
most infections asymptomatic
Disease is rare
Infectious dose < 100 virions

Question 25

Vaccines

Answer 25

Oral polio vaccine 1 dose
Polio shot(IPV) 4 doses