Retroviruses

Question 1

What is a retrovirus?

Answer 1

> Unique enzyme (reverse transcriptase) which generates a DNA intermediate which is then integrated into the host genome (called a provirus)
New viral genomes produced by cellular transcriptional machinery

Question 2

Describe the genomic organisation of retroviruses

Answer 2

Gene order in all retroviruses is always the same —

5’ — gag - pol - env — 3’

Gag: codes for proteins which make up the matrix, capsid, and nucleoprotein structures
Pol: codes for reverse transcriptase and integrase and protease enzymes
Env: codes for the surface and transmembrane components of the viral envelope protein (Env)

Question 3

Explain the role of reverse transcriptase in retroviruses

Answer 3

transcription of viral genome RNA to DNA

Question 4

Explain the role of integrase in retroviruses

Answer 4

integration of the ds DNA into the host genome to form the provirus

Question 5

Explain the role of protease in retroviruses

Answer 5

following release of new virion, cleavage of certain proteins is required for viral maturation (required to enter next host cell) and infectivity

Question 6

What is the function of the ‘gag’ gene in retroviruses?

Answer 6

Gag: codes for proteins which make up the matrix, capsid, and nucleoprotein structures

Question 7

What is the function of the ‘pol’ gene in retroviruses?

Answer 7

Pol: codes for reverse transcriptase and integrase and protease enzymes

Question 8

What is the function of the ‘env’ gene in retroviruses?

Answer 8

Env: codes for the surface and transmembrane components of the viral envelope protein (Env)

Question 9

Give examples of viruses that are associated with the development of cancer

Answer 9

> EBV
Kaposi’s sarcoma-associated herpesvirus (KSHV)
Human papilloma virus (HPV)
HBV/HCV
Merkel cell polyomavirus >Human T-cell leukemias virus type 1 (HTLV-1)

Question 10

What can infection with HTLV-1 cause?

Answer 10

Adult T-cell leukaemia, HTLV-1 associated myelopathy (HAM, AKA tropical spastic paraparesis)

Question 11

Where is the virus HTLV-1 endemic?

Answer 11

Central + South America
The Caribbean
Melanesia
Central + South Africa

Question 12

What can infection with HTLV-2 cause?

Answer 12

Hairy cell leukaemia (with latency of 20-30 years)

Question 13

What is hairy cell leukaemia?

Answer 13

Leukaemia cells collect in the spleen and cause splenomegaly

and marrow can’t produce enough normal WBCs –> infection susceptibility. Associated with HTLV-2 infection