Virus Assembly & Release 1

Question 1

Where does Herpes virus assemble?

Answer 1

Nucleus

Question 2

Where do Picornaviruses and Poxviruses assemble?

Answer 2

Cytoplasm

Question 3

Where to Retroviruses assemble?

Answer 3

Cytoplasm AND plasma membrane

Question 4

Examples of poxviruses

Answer 4

Vaccinia, smallpox

- use cytoskeleton to move plasma membrane and away from the cell

Question 5

What are the stages of formation of vaccinia virus (poxvirus)

Answer 5

• crescents form intact membrane vesicle containing granular matrix
• nucleoprotein produced

Question 6

What are the 4 different type of Vaccinia virions?

Answer 6

IMV - 1 membrane, retained in cell
IEV - 3 membranes, movement to cell surface
CEV - 2 membranes, induces formation of actin tails to drive CEV away from cell
EEV - 2 membranes, long-range spread

Question 7

How many Kb in Herpesvirus?

Answer 7

approx. 150kb

Question 8

How does a herpesvirus assemble?

Answer 8

• requires scaffold proteins & non-capsid proteins
• concatenated DNA cut to single length
• capsids get membrane by budding through nuclear membrane
• only full capsids enveloped

Question 9

How does a herpesvirus reach the cell membrane?

Answer 9

• Fuses with nuclear membrane to get between 2 membranes
• fuses with outer nuclear membrane
• associate with membrane in cytoplasm - buds into it
• taken to cell surface

Question 10

What are the features of Poliovirus?

Answer 10

• non-enveloped
• icosahedral
• • sense ssRNA
• 5’ end VPg (22aa)
• single ORF encodes 2200aa polyprotein
• proteolitically cleaved

Question 11

What are the 3 components poliovirus is cleaved into?

Answer 11

• P1 - VP0 (VP4,VP2), VP3, VP1
• P2 - 2A protease (initial P1,2,3 cleavage)
• P3 - 3C protease

Question 12

What change occurs to the poliovirus protein?

Answer 12

• myristoylated
• addition of 14C saturated fatty acid to N-terminal glycine residue
• irreversible amide link
• catalysed by NMT

Question 13

What happens to P1 in poliovirus?

Answer 13

• gets cleaved by 3C protease
• HSP70 chaperone
• forms protomer (5S), VP0, VP1, VP3

Question 14

Why does poliovirus need to be myristilated?

Answer 14

So that pentamers can form properly

stabilised by interaction between N-termini of VP3 and myristate residues on VP0

Question 15

How many pentamers make up the poliovirus procapsid

Answer 15

12 pentamers make a 73S procapsid

Question 16

How is poliovirus RNA genome encapsidated?

Answer 16

• only VPg-RNA can be encapsidated
• VPg is an encapsidation signal to recognise right RNA
• majority of particles are EMPTY (lots of RNA without VPg)
• SOMETIMES - associate with site of RNA replication, make 140S provirion

Question 17

Where does poliovirus encapsidation take place?

Answer 17

• 2C and 2BC reorganise cellular membranes into virus factories
• 2C ATPase binds to 3’ end of genome RNA
• 2B ion channel proten - membrane permeability

Question 18

What is the poliovirus virion composed of?

Answer 18

ONLY VPg-RNA and VP1-4
maturation occurs after encapsidation - cleavage of VP0 to VP4 and VP2
cleavage requires GSH

Question 19

What are the benefits of a mature poliovirus particles compare to the proviron?

Answer 19

more resistant to

• pH
• heat
• detergents

Question 20

How does poliovirus/rhinovirus inhbition cellular cap-dependent translation?

Answer 20

• 2A protease cleaves eIF4G
• G is cleaved
• inhibits the initiation of translation = host cell shut-off
• apoptosis occurs

Question 21

Why is the inhibition of cellular cap-dependent translation so clever?

Answer 21

• Viral protein synthesis continues due to the IRES whilst cellular proteins are not translated
• Virus doesn’t have the cellular cap

Question 22

How are poliovirus particles released

Answer 22

• Lysis release
• 25,000 - 100,000 per cell
• 1:1000 infectivity:particle