Virus Genomes Flashcards
SsRNA can be positive sense, negative sense or ambisense. Describe what each term means.
Positive sense - same RNA sequence (polarity) as the mRNA
Negative sense - opposite polarity (nucleotide sequence) from the mRNA
Ambisense - mixture of the two
Polyanion is …..
Nucleic acid associates with basic proteins to facilitate packaging
What structure behaves like eukaryotic polyanion in viruses?
Nucleocapsid
What are the constraints for an RNA in animal cell?
Cells cannot make DNA or RNA from an RNA template so cannot replicate in nucleus or cytoplasm without viral factors.
What are the constraints for a DNA genome?
both replicating and transcribing DNA in the nucleus so either must get the DNA into the nucleus or make their own polymerases.
What are the ways in which virus overcome the eukaryotic cells monocistronic way of translating messages?
Cleavable polypeptide
Different message for each protein
Make sure polycistronic messages can be read
What modifications allow vRNA to be recognised by host cells and to function as mRNA?
5’ end methylation nucleotide cap
3’ end polyadenylation
What type of RNA is directly infectious in the absence of virus proteins?
Positive sense RNA
In eukaryotes, the virus RNA (+)strands are often modified. TRUE or FALSE?
TRUE
UTR at the 5’ and 3’ end stands for?
Untranslated region
In caliciviruses, each mRNA codes for different proteins. Name the mRNA and what it codes for.
MRNA1 - non structural enzymic function
MRNA 2&3 - viral structural proteins
Single mRNA made and a polyprotein is translated. A viral protease in the polyprotein cleaves the polyprotein to make viral proteins
What virus does this?
Picornavirus
Single mRNA made but contains internal ribosome entry sites.
What virus is responsible for this?
IRES
List major differences between positive stranded viruses and negative stranded viruses.
Negative stranded viruses:
- segmentation common
- larger genomes
- more diverse
- replication more complicated
- RNA genome non infectious as purified RNA
- all virus particles contain a virus specific polymerase
- form positive sense transcripts
- or a double stranded molecule known as the replication form or the replicative intermediate which serve as template for further rounds of mRNA synthesis
What is a segmented genome virus?
2 or more pieces of nucleotides packaged in the same particle e.g. Orthomyxo viruses, flu, packaging problem
Give example of multipartite virus.
bipartite Comovirus
what are multipartite genomes
Segmented virus but each segment is contained within a different particle and both particles can infect the cell
How ambisense genome is translated?
GP/Z gene - positive sense so translated directly
L/NP gene - negative sense so requires
RNA transcription before translation
Describe bacteriophage M13 genome
6.4 kb Ss circular DNA 10 genes Positive strand 90% genome coding
-Strand DNA synthesis transcribed to make mRNA and then proteins
Gene 5 switched to rolling circle
Describe phage lambda genome
Linear ds DNA
50 Kb
Cohesive ss DNA termini - 12 nucl long
Concatemers formed and then resolved to reconstitute genome
Important sequences at the end of the linear viral genome are very common
Describe Phage 4 genome
Larger linear ds DNA
160kb
Terminal redundancy - common feature of linear genomes
Direct repeat
Primer RNA at 5’ end = genomes shorter = during replication concatemers formed = endonuclease recognises and cuts at the terminal redundancy which is then regenerated
Crime adenovirus genome
30-38 kb
Linear ds genome infecting eukaryotes - medium
30-40 proteins
Genetically similar to infected host cell
Inverted repeats terminal sequences
Complicated functional structures can form - cruciform and hairpins
