Retroviruses I

Question 1

Function of:

1. RT
2. RNase H
3. integrase
4. protease

Answer 1

1. reverse transcriptase- creates cDNA from RNA
2. degrades RNA after DNA is created
3. puts DNA into host chromosome
4. cuts precursors

Question 2

Function of:

1. GP41
2. GP120
3. How are they connected?

Answer 2

1. transmembrane protein that facilitates merging of cell membranes
2. on outside of membrane, binds host cell
3. not covalently linked, so GP120 can dissociated from GP41 –> inactivation

Question 3

Retrovirion structure

1. Describe
2. What are gag proteins?
3. How many RNA strands are in the capsid? What polarity are they?

Answer 3

1. lipid bilayer with a nucelocapsid (made of gag proteins) which encloses genetic material
2. Group Specific Antigens, packaged with RNA molecules
3. 2 identical negative strand RNA

Question 4

Retrovirus Life Cycle (5 steps)

Answer 4

1. Virus entry
2. Reverse transcription
3. Integration
4. assembly
5. budding

Question 5

1. What is the role of GP120 in membrane fusion?

2. What is the role of GP41 in membrane fusion?

Answer 5

1. binds CD4 on cell and brings membranes closer

2. inserts into host cell membrane and retracts (hairpin fashion), causing fusion

Question 6

1. Why are co-receptors important?
2. What co-receptor is missing in individuals that are “resistant” to HIV?
3. Who has this deletion?

Answer 6

1. important for virus binding
2. CCR5
3. some individuals of european ethnicity

Question 7

1. What is the order of genes on the RNA?
2. What is the function of virion RNA?
3. What binds at the 5’ end?
4. What does the 3’ end act as?

Answer 7

1. gag-pol-env
2. template for DNA
3. host derived tRNA
4. primer for synthesis

Question 8

1. Where does the RNA insert?

2. What is the LTR region and what does it act as?

Answer 8

1. at random

2. where virion DNA and host DNA meet; acts as a promoter for RNA polymerase II –> transcription

Question 9

What are 5 possible outcomes of proviral cDNA integration into the host cell?

Answer 9

1. proviral DNA is not transcribed and infection is latent
2. integration occurs in germ line cell –> endogenous virus (vertically transmitted)
3. integration occurs within and disrupts an essential gene –> cell death (rare)
4. integration occurs adjacent to a cellular oncogene, cell transformation may occur
5. transcription of provirus –> productive infection

Question 10

1. What is the role of DNA ligase in proviral cDNA integration?
2. Polymerase?
3. Define Latency

Answer 10

1. connects strands of cDNA and host DNA
2. fills in the gaps
3. existence of viral nucleic acid in cell w/o producing virus

Question 11

What are some diseases that can be treated with gene therapy using retroviruses?

Answer 11

1. adenosine deaminase severe combied immunodeficiency

2. X-linked SCID

Question 12

1. What happens after the provirus is integrated into the cell?
2. What does the mRNA code for?
3. What protein is made the most?
4. How is other protein made?
5. What binds gag?
6. How are envelope glycoproteins made?

Answer 12

1. it is transcribed and many mRNA copies are made
2. gag-pol-env: gag proteins, polymerase, envelop proteins
3. gag
4. stop codon after gag is skipped, so gag and pol are created;
5. RNA
6. made in ER and accumulate in the budding site on cell membrane

Question 13

What protein is required for a Virus to be infectious? why?

Answer 13

Protease;

cleaves gag proteins to allow infectious activity and capsid maturation

Question 14

What does Highly-Active Anti-Retroviral Therapy use to inactivate the virus?

Answer 14

Protease inhibitors