Virus Genetics

Question 1

Which virus has the fewest genes? How many?

Answer 1

Parvovirus

2 genes

Question 2

What virus has 3 genes?

Answer 2

Retrovirus

Question 3

What virus has 8 genes?

Answer 3

Papilloma

Question 4

What virus has 10 genes and is double stranded?

Answer 4

Adenovirus

Question 5

What virus has 70-100 genes?

Answer 5

Herpesvirus

Question 6

What virus has the greatest number of genes? How many?

Answer 6

Poxvirus

200 genes

Question 7

How is expression of viral genes induced? How is it not induced?

Answer 7

• induced by txn factors binding to promoter region

- not induced by binding of repressor/inducer to operator

Question 8

Are viral genes eukaryotic or prokaryotic?

Answer 8

eukaryotic

Question 9

How do viruses have tissue specificity?

Answer 9

promoters of viral genes are only recognized by txn factors which are expressed in particular tissues

Question 10

Describe the simple genome of retroviruses

Answer 10

genes are linear
one RNA strand
single promoter

Question 11

Describe the complex genome of adenoviruses, herpesviruses, and poxviruses

Answer 11

genes on both strands of DNA
genes often overlap
each gene has own promoter

Question 12

What 5 aspects make viral genomes efficient?

Answer 12

No non-coding regions
Overlapping reading frames
Translational frameshifts 
Alternate splicing
Polyproteins

Question 13

What cleaves polyproteins into individual proteins? In what viruses is this an especially good drug target?

Answer 13

viral protease

HIV, Hep C

Question 14

Which are stable - DNA or RNA viruses?

Answer 14

DNA stable

Question 15

What are 3 reasons why RNA viruses are not stable, and have a lot of mutations?

Answer 15

error prone RNA pol
No Pol proofreading
some lack 2nd strand - mutation continues

Question 16

What kinds of mutations happen frequently in viruses? Which kind happens infrequently?

Answer 16

• Frequent: pt mutations, deletions, integration into host genome, recombination, rearrangement, insertion
• Infrequent: insertions into viral genome

Question 17

How have mutations allowed the measles vaccine to be created?

Answer 17

• so many mutations the host range changed completely

- then non-human strain used to make human vaccine

Question 18

To what drug have herpes simplex mutants become resistant?

Answer 18

Ancyclovir

Question 19

To what class of drug have HIV or Hep C mutants become resistant?

Answer 19

protease inhibitors

Question 20

To what drug have influenza mutants become resistant?

Answer 20

Amantidine

Question 21

What are 5 common phenomena which happen when 2 viruses infect the same cell? Which happens most?

Answer 21

Complementation, Phenotypic Mixing, Recombination, Reassortment, Interference (happens most)

Question 22

What is viral complementation? What is an example?

Answer 22

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

Question 23

what is viral phenotypic mixing? What is an example?

Answer 23

exchange of capsids

ex. 2 polio virus serotypes infect same cell –> end up with capsids which are a mix of both serotypes

Question 24

Are the capsid changes seen in viral phenotypic mixing passed on to next generation?

Answer 24

No

Question 25

What does phenotypic mixing produce?

Answer 25

pseudotype - genetic material of one virus in capsid or envelope of another

Question 26

What is viral recombination? What does it produce?

Answer 26

- exchange of genes by crossing over at regions of homology | - hybrid virus

Question 27

What is an example of viral recombination to produce a hybrid virus?

Answer 27

Eastern equine encephalitis + Sindbis virus = Western equine encephalitis

Question 28

Which forms of virus interaction (when 2 viruses infect same cell) change the genome to produce new strains? Which do not (next gen reverts)?

Answer 28

change genome: recombination, reassortment | don't change genome: complementation, phenotypic mixing, pseudotyping

Question 29

What is viral interference? How is it accomplished (3 ways)?

Answer 29

infection by one virus prevents infection by another - block receptors - compete for resources - produce interferon or other anti-viral agents (stim innate immunity)

Question 30

What kind of disorders are mist likely to be treated by gene therapy?

Answer 30

monogenic (one gene)

Question 31

What are examples of monogenic disorders which might be treated by gene therapy?

Answer 31

``` CF autoimmune Hemophilia (successful in dogs) Liver enzyme-deficiency Retinal disorders (successful in mice) ```

Question 32

In what two species has gene therapy been successful? What was treated?

Answer 32

dogs - hemophilia | mice - retinal disorder

Question 33

What are the four categories of host range mutant viruses used for gene therapy?

Answer 33

retroviruses adenoviruses adeno-associated herpes simplex

Question 34

What are 4 problems seen with gene therapy?

Answer 34

- short duration of expression - low efficiency of gene transfer - severe inflammation in response to virus - insertion of virus into genome --> malignant disease