Virus Genetics Flashcards
Which virus has the fewest genes? How many?
Parvovirus
2 genes
What virus has 3 genes?
Retrovirus
What virus has 8 genes?
Papilloma
What virus has 10 genes and is double stranded?
Adenovirus
What virus has 70-100 genes?
Herpesvirus
What virus has the greatest number of genes? How many?
Poxvirus
200 genes
How is expression of viral genes induced? How is it not induced?
- induced by txn factors binding to promoter region
- not induced by binding of repressor/inducer to operator
Are viral genes eukaryotic or prokaryotic?
eukaryotic
How do viruses have tissue specificity?
promoters of viral genes are only recognized by txn factors which are expressed in particular tissues
Describe the simple genome of retroviruses
genes are linear
one RNA strand
single promoter
Describe the complex genome of adenoviruses, herpesviruses, and poxviruses
genes on both strands of DNA
genes often overlap
each gene has own promoter
What 5 aspects make viral genomes efficient?
No non-coding regions Overlapping reading frames Translational frameshifts Alternate splicing Polyproteins
What cleaves polyproteins into individual proteins? In what viruses is this an especially good drug target?
viral protease
HIV, Hep C
Which are stable - DNA or RNA viruses?
DNA stable
What are 3 reasons why RNA viruses are not stable, and have a lot of mutations?
error prone RNA pol
No Pol proofreading
some lack 2nd strand - mutation continues
What kinds of mutations happen frequently in viruses? Which kind happens infrequently?
- Frequent: pt mutations, deletions, integration into host genome, recombination, rearrangement, insertion
- Infrequent: insertions into viral genome
How have mutations allowed the measles vaccine to be created?
- so many mutations the host range changed completely
- then non-human strain used to make human vaccine
To what drug have herpes simplex mutants become resistant?
Ancyclovir
To what class of drug have HIV or Hep C mutants become resistant?
protease inhibitors
To what drug have influenza mutants become resistant?
Amantidine
What are 5 common phenomena which happen when 2 viruses infect the same cell? Which happens most?
Complementation, Phenotypic Mixing, Recombination, Reassortment, Interference (happens most)
What is viral complementation? What is an example?
When 2 viruses infect same cell, a gene funtion of 1 virus makes up for a mutated/missing gene of the other
ex. Hep B and Hep D must grow together
what is viral phenotypic mixing? What is an example?
exchange of capsids
ex. 2 polio virus serotypes infect same cell –> end up with capsids which are a mix of both serotypes
Are the capsid changes seen in viral phenotypic mixing passed on to next generation?
No
What does phenotypic mixing produce?
pseudotype - genetic material of one virus in capsid or envelope of another
What is viral recombination? What does it produce?
- exchange of genes by crossing over at regions of homology
- hybrid virus
What is an example of viral recombination to produce a hybrid virus?
Eastern equine encephalitis + Sindbis virus = Western equine encephalitis
Which forms of virus interaction (when 2 viruses infect same cell) change the genome to produce new strains? Which do not (next gen reverts)?
change genome: recombination, reassortment
don’t change genome: complementation, phenotypic mixing, pseudotyping
What is viral interference? How is it accomplished (3 ways)?
infection by one virus prevents infection by another
- block receptors
- compete for resources
- produce interferon or other anti-viral agents (stim innate immunity)
What kind of disorders are mist likely to be treated by gene therapy?
monogenic (one gene)
What are examples of monogenic disorders which might be treated by gene therapy?
CF autoimmune Hemophilia (successful in dogs) Liver enzyme-deficiency Retinal disorders (successful in mice)
In what two species has gene therapy been successful? What was treated?
dogs - hemophilia
mice - retinal disorder
What are the four categories of host range mutant viruses used for gene therapy?
retroviruses
adenoviruses
adeno-associated
herpes simplex
What are 4 problems seen with gene therapy?
- short duration of expression
- low efficiency of gene transfer
- severe inflammation in response to virus
- insertion of virus into genome –> malignant disease
