[W3] Poxviruses Flashcards
What are the two subfamilies of poxviruses?
Chordopoxvirinae (infect vertebrates) and Entomopoxvirinae (infect invertebrates).
Which subfamily contains medically important viruses?
Chordopoxvirinae.
What is the shape and size of poxvirus particles?
Oval or brick-shaped, 200–400 nm long.
What are key structural features of the vaccinia virus (VACV) particle?
- Lipid-protein outer surface
- Biconcave core
- Two lateral bodies
- Highly complex with >100 proteins.
What are the two forms of mature poxvirus virions?
Intracellular mature virions (IMV) with one membrane and extracellular enveloped virions (EEV) with two membranes.
Describe the poxvirus genome.
Linear dsDNA, 130–375 kb, ~200 genes, flanked by covalently closed inverted terminal repeats (ITRs).
Where does poxvirus replication occur and why is this unusual?
In the cytoplasm, which is unusual for a DNA virus.
How long does the poxvirus replication cycle take?
Approximately 12 hours.
What enables poxvirus entry into host cells?
The Entry-Fusion Complex with 4 attachment and 11 fusion proteins.
How does uncoating occur?
In two stages: outer membrane removal during entry, then core uncoating in cytoplasm.
How is vaccinia virus gene expression temporally regulated?
Into early, intermediate, and late phases.
Where does early gene expression occur and what is unique about it?
In the cytoplasm within the partially uncoated core, using virion-contained transcription machinery.
What triggers intermediate and late gene expression?
- Intermediate requires early gene products
- Late requires intermediate gene products.
What enzymes are used to cap viral mRNA?
- Terminal phosphatase
- Guanylyltransferase
- N7-methyltransferase
- 2’-O-methyltransferase.
Why is mRNA splicing not needed in poxviruses?
Viral mRNA is made in the cytoplasm and lacks introns.
How does poxvirus translation affect host protein synthesis?
Host synthesis is inhibited; translation shifts to viral polypeptides.
How do viral mRNAs initiate translation without eIF4G?
Their short, unstructured 5’ UTRs allow initiation with low eIF4F requirements.
What is the function of the D10 protein?
Acts as an mRNA decapping enzyme, downregulating host gene expression.
What model describes poxvirus genome replication?
The self-priming model involving concatemer formation and resolution.
What are cytoplasmic factories?
Sites in the cytoplasm where viral replication and assembly occur.
What do poxviruses use as primers in replication?
3’ ends generated from single-strand nicks near hairpin loops.
What is the function of hairpin loops and ITRs?
Important for self-priming DNA replication.
What is the immature virion (IV)?
Spherical particle formed during initial assembly.
How is the intracellular mature virion (IMV) formed?
IV matures into IMV, which is released upon cell lysis.
