Retroviruses

Question 1

Key features of retroviruses

Answer 1

• two copies of RNA genomre in each viral particle
• reverse transcribe RNA to DNA
• DNA “provirus” integrates into cellular DNA
• establish PERSISTENT infections

Question 2

A simple retrovirus genome

Answer 2

gag pol env
core structural proteins
enzymes for replication reverse transcriptase, integrase, protease
envelope glycoproteins

Question 3

Retroviruses infect cells by binding to a receptor

Replication:

Answer 3

Integration is necessary for a productive viral lifecycle

• simple retroviruses (eg FeLV) integrate in dividing cells
• lentiviruses (egHIV) can integrate in non-dividing cells

Question 4

Persistent infections

Answer 4

• integration of the provirus
• persistence in the genome (no disease in many cases)
• maximises chance of viral transmission to new host
• ALL retroviruses integrate

Question 5

Retroviral Assembly

Answer 5

-some retroviruses assemble at the pericentriolar region of the nucleus, then fully assembled particle then migrating to the cell surface

Question 6

FeLV-discovered in Glasgow

Answer 6

• can cause immunosuppression, tumours, anaemia
• 3 subgroups: A, B and C, classified according to the viral envelope glycoprotein (gp70)
• FeLV-A - subgroup isolated from all infected cats
• FeLV- B and C subgroups are generated within the host
• vaccines available

Question 7

Bovine Leukaemia Virus

Answer 7

-Causes enzootic bovine leukosis
• Virus latently infects B lymphocytes
• No free virus in blood
• Antibodies in persistently infected cattle
• Viral Tax protein trans-activates cellular genes
• Products of trans-activated cell genes may be oncogenic

Question 8

Bovine Leukaemia Virus

Answer 8

• transmission via milk, blood

- vertical or horizontal transmission

Question 9

Oncogenic retroviruses

Answer 9

• a Avian leukosis viruses (ALV)
• b Jaagsiekte sheep retrovirus (JSRV)
• Feline leukaemia virus (FeLV)
• Bovine leukaemia virus (BLV)

Question 10

Mechanisms of retroviral oncogenesis

Answer 10

• oncogene capture and transduction
• insertional activation
• other mechanisms

Question 11

Rapid oncogenic transformation: in vitro

Answer 11

Infection with oncogenic virus (e.g. Rous sarcoma virus)

• loss of contact inhibition
• increased growth rate

Question 12

Human Immunodeficiency Virus

Answer 12

origin chimpanzee?

Question 13

Endogenous retroviruses (ERVs)

Answer 13

• genomes persist in host DNA

- transposable (mobile)

Question 14

Retroviruses as clinical tools

Answer 14

-gene therapy

Question 15

Integration of DNA provirus

Answer 15

• may lead to cancer

- exploited for gene therapy

Question 16

Rous sarcoma virus replication dependent on DNA

Answer 16

• RNA genome

- Actinomycin D inhibits transcription and hence RNA synthesis

Question 17

Transmission of retroviruses

Answer 17

• lipid envelope renders retroviruses labile
• susceptible to desiccation and detergents
• close contact transmission