Viral Genetics Flashcards
Size of viruses vary: anywhere from 2 genes to 200 genes. Which are the smallest and biggest viruses?
Parvovirus only has 2 genes (DNA virus: so use host DNA polymerase); Poxvirus has around 200 genes (DNA: so use own DNA polymerase)
T/F: Viruses are eukaryotic like humans. They have multiple transcription factors and has complicated regulation.
True
T/F: Viruses are small, but are very efficient
True; no space is wasted because about 100% of genome is doing something.
What is the significance of viral reading frames overlapping
can make a lot of diff proteins from small genome
What are 5 reasons why virus genomes are efficient?
1) abt 100% of genome is doing something
2) reading frames overlap
3) ribosomal frameshifting
4) alternative splicing of RNA
5) cleavage of polyproteins by viral proteases
T/F: All types of mutations can occur in viruses (point, deletion, etc)
True
What are 2 useful consequences of viral mutations?
1) track progress of virus thru pop (epidemiologic studies)
2) allow live vaccines to be made by basing it on mutation
What are 3 negative consequences of viral mutations?
1) produce new antigens that will evade immunity
2) can lead to drug resistance
3) integration of viral genome can cause disease
What are the 4 types of virus interactions we talked about?
1) complementation
2) phenotypic mixing
3) recombination
4) reassortment
Describe the following type of virus interaction: 2 viruses need both XY genes to replicate. Virus A only has X and virus B only has Y. They can’t do anything alone, but when put together, they can. What about their progenies?
This is an example of complementation. Their progenies will not be able to replicate.
Explain phenotypic mixing
Virus A and Virus B will infect cells at the same time. Progenies will look like A and B and some will be pseudotypes with A or B genome but a mixture of switched glycopeptides.
It is very unusual for cells to be infected by 2 viruses b/c
of viral interference:
1) block receptors once a virus is already in
2) competition for resources
3) stimulation of innate immunity
What are some problems with gene therapy?
1) viruses’ effect doesn’t last very long/does not spread past injection site
2) transient expression of foreign gene (will deplete so no long term effects)
3) requires very high doses of virus vectors
4) inflammatory response to virus vector
What are 2 diseases we talked about in class that have some successful gene therapy in animal trials?
1) retinal d/os: colorblind monkeys injected with L-opsin gene in adeno-associated virus vector
2) hemophilia: transfer factor VIII by viral vector in dogs improved clotting time
