Viruses Flashcards
How many coat protein subunits does a TMV particle have?
2130
How does the 20S disk allow recognition of homologous viral RNA?
Provides long stretch of nucleotide binding sites for interaction with specific RNA sequence
Who discovered the origin of assembly?
Zimmern 1977
How is viral elongation bidirectional?
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
Co-translational and co-replicational disassembly
- 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
Brome mosaic virus infectious clone
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
Brome mosaic virus 3 particles
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)
Three virus-encoded enzymes involved in replication of positive-sense RNA viruses
- Helicase - separates and straightens RNA strands during replication
- Methyltransferase - transfers 5’ cap to end of viral RNAs
- RNA-dependent RNA polymerase
What do Potyviruses have at their 5’ end?
A protein, no 5’ cap
What genome does Cauliflower mosaic virus have?
dsDNA, replicated by reverse transcription of a pregenomic RNA
Proteins encoded by CaMV genome
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
CaMV transcription and protein synthesis
- 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
Cauliflower mosaic virus replication
- Uses reverse transcription using 35S RNA as a template
- As it does this it makes more copies of itself
- Uses rRNA as primers