Viruses

Question 1

How many coat protein subunits does a TMV particle have?

Answer 1

2130

Question 2

How does the 20S disk allow recognition of homologous viral RNA?

Answer 2

Provides long stretch of nucleotide binding sites for interaction with specific RNA sequence

Question 3

Who discovered the origin of assembly?

Answer 3

Zimmern 1977

Question 4

How is viral elongation bidirectional?

Answer 4

5’ end is pulled through central hole and rapid elongation ensues
3’ end is slower due to the types of protein aggregates that are used to assemble the particle

Question 5

Co-translational and co-replicational disassembly

Answer 5

• Once inside a plant cell, there is a different pH and concentration of calcium ions, so the coat proteins lose protons and Ca2+ ions
• Loss of charge results in weakening of the virus coat at the 5’ end
• Ribosomes bind to the 5’ end and begin moving down the RNA, which strips off the coat proteins
• The replicase proteins are translated and begin translating from the 3’ end
• As they replicate the virus, they strip off the remaining coat proteins

Question 6

Brome mosaic virus infectious clone

Answer 6

Strong tool for studying plant viruses
Convert positive-sense RNA to double-stranded cDNA using reverse transcriptase
Have cDNA copy of viral genome carried in a bacterial plasmid

Question 7

Brome mosaic virus 3 particles

Answer 7

Particle 1: RNA1 - P1 (methyltransferase and helicase)
Particle 2: RNA2 - P2 (RNA polymerase)
Particle 3: RNA3 - P3a and P3b (movement and capsid)
RNA4 - subgenomic P3b/P4 (capsid)

Question 8

Three virus-encoded enzymes involved in replication of positive-sense RNA viruses

Answer 8

1. Helicase - separates and straightens RNA strands during replication
2. Methyltransferase - transfers 5’ cap to end of viral RNAs
3. RNA-dependent RNA polymerase

Question 9

What do Potyviruses have at their 5’ end?

Answer 9

A protein, no 5’ cap

Question 10

What genome does Cauliflower mosaic virus have?

Answer 10

dsDNA, replicated by reverse transcription of a pregenomic RNA

Question 11

Proteins encoded by CaMV genome

Answer 11

Cell-to-cell movement protein (P1)
Two aphid transmission factors (P2 & P3)
Precursor of capsid proteins (P4)
Polyprotein precursor of proteinase, reverse transcriptase and ribonuclease H (P5) (separates RNA from cDNA)
Inclusion body protein/translational transactivator

Question 12

CaMV transcription and protein synthesis

Answer 12

• Discontinuities, gaps close in nucleus when dsDNA associated with histones
• Minichromosome is transcribed by the host-dependent RNA polymerase
• 2 promoters: 19S (weak) and 35S (strong)
• P6 translated from monocistronic 19S RNA
• P6 protein allows ribosomal shunting - associates with RNA and shunts ribosome to next start codon, allowing silent ORFs to be translated

Question 13

Cauliflower mosaic virus replication

Answer 13

• Uses reverse transcription using 35S RNA as a template
• As it does this it makes more copies of itself
• Uses rRNA as primers