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MICR2121 Molecular Virology > Virus Assembly and Release > Flashcards

Virus Assembly and Release Flashcards

1
Q

Give 4 obstacles in assembling a virus particle

A
  1. Getting all components to the site of assembly
  2. Select those components from cellular proteins and nucleic acids
  3. Assembly into infectious virus particles
  4. Release from the cell
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2
Q

Where does Pox virus replicate?

A

In the cytoplasm

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3
Q

How does Pox virus get to the plasma membrane?

A

Using the cytoskeleton (microtubules and actin filaments)

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4
Q

What are the names of the 4 different types of virions and how many membranes do they have?

A
  1. Intracellular mature virus (1)
  2. Intracellular enveloped virus (3)
  3. Cell associated enveloped virus (2)
  4. Extracellular enveloped virus (2)
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5
Q

what does capsid assembly of Herpes virus require?

A

Scaffold proteins

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6
Q

How does Herpes Virus reach the plasma membrane?

A

Replicates in the nucleus,
Taken into capsid,
Bud into the nuclear membrane to pick up tegument proteins,
Fusion with nuclear membrane releasing virion into cytoplasm,
Fuses with membrane of a cellular compartment to form an exocytotic vesicle

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7
Q

What is covalently attached to the 5’end of poliovirus RNA?

A

VPg

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8
Q

What does P1 encode in poliovirus?

A

All structural proteins

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9
Q

What cleaves P1?

A

3C

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10
Q

what does Myristoylated mean?

A

Addition of a 14-C saturated fatty acid to an N-terminal glycine by an amide linkage catalysed by N-myristoyltransferase

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11
Q

Which P1 proteins form the protomer and how many in a pentamer?

A

VP0, VP3, VP1

5

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12
Q

How is the pentamer stabilised?

A

Interactions between the N-termini of VP3 and myristate residue on VP0

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13
Q

How is the PV genome encapsidated?

A

2C ATPase brings the RNA to the site of capsid entry

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14
Q

What is the role of 2C and 2BC proteins in PV?

A

Reorganising cellular membranes into vesicles where virus assembly takes place

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15
Q

What is 2B?

A

An ion channel protein. Alters membrane permeability

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16
Q

What is VP0 cleaved into and why?

A

VP4 and VP2

Stabilises the mature virion

17
Q

How does PV inhibit cellular cap-dependent translation?

A

2A protease cleaves eIF4G (component of eIF4F), shuts the host cell protein synthesis off

18
Q

How do retroviruses express their structural proteins?

A

The ORFs are separate, gag and pol are spliced out so the 1st AUG is for env

19
Q

How are gag and pol expressed in different quantities?

A

Ribosome can bounce over the gag stop codon creating a fusion protein which encodes pol (5%) or 95% of the time just reads upto the gag stop codon and falls off

20
Q

What does the Gag-Pol fusion protein encode?

A

Protease, reverse transcriptase, integrase

21
Q

Where does Gag myristate insert?

A

Into the lipid bilayer stabilised by electrostatic interactions (does not interact with the amino acids sequence)

22
Q

What cleaves env into gp120 (surface glycoprotein) and gp41 (transmembrane glycoprotein)?

A

Furin

23
Q

What forms a trimer?

A

3 gp120 and 3 gp41

24
Q

How do gp120 and gp41 associate?

A

Through non-covalent bonds

25
Q

where is the HIV packaging signal located?

A

Between the LTR and Gag coding sequence

26
Q

What recognises the packaging signal?

A

Nucleocapsid proteins

27
Q

What is the packaging signal?

A

Complex secondary structure, 4-stem loops specifically bound by NC (p7) of p55Gag

28
Q

How do capsid and envelope glycoproteins associate to form a virus particle?

A

Gp120 and Gp41 trimer is absorbed into mini-vesicles of the MVB.
HIV Gag recruites ESCRT complex (builds vesicles) by interaction with P6
HIV is released via MVBs

29
Q

How does HIV mature?

A

Cleavage of Gag and Gag-Pol to individual peptides after release?

30
Q

Give 3 accessory proteins which are incorporated?

A

Vpr (interacts with p6)
Vif (infectivity factor)
Nef (myristoylated and membrane associated)

31
Q

Name a cellular protein which is incorporated and what it does?

A

Cyclophilin A (CyPA)
Peptidyl-propyl isomerase
Ensure correct folding of proteins in proline rich regions

32
Q

Give 3 things which occur in both PV and HIV

A
  1. Require myrisoylation of structural proteins (PV VP4, HIV p17MA)
  2. Require proteolytic cleavage of polyprotein
  3. Require membrane structures for assembly

MICR2121 Molecular Virology (14 decks)

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