Reverse Transcriptase Viruses (Retroviruses)

Question 1

Subfamilies of retroviridae (3):

Answer 1

• Oncovirinae
• Lentivirinae
• Spumavirinae

Question 2

Retroviridae (3):

Answer 2

• Helical nucleocapsid plus icosahedral or cylindrical outer capsid (complex structure).
• 2 SS +RNA (35S joined by tRNA).
• Enveloped

Question 3

The four internal capsid proteins are encoded by:

Answer 3

GAG gene.

Question 4

Retroviridae RNA genome consists of (4):

Answer 4

GAG - Pol - Env - ONC (+/-)

Question 5

Retroviridae replication (3):

Answer 5

• +RNA genome used to make -DNA.
• -DNA used to form a provirus with +DNA.
• Provirus integrated at many sites via integrase.

Question 6

Long terminal repeats (3):

Answer 6

LTRs:

• Produced by the conversion of RNA to proviral DNA.
• Located at each end of the provirus.
• Contain regulatory regions.

Question 7

Transcription of Retroviridae from provirus can yield 3 mRNAs:

Answer 7

• 35S mRNA.
• 28S mRNA
• 21S mRNA (oncoprotein, +/-)

Question 8

Retroviridae translation of mRNAs (3):

Answer 8

• 35S mRNA GAG or GAG - Pol polyprotein.
• 28S mRNA Env polyprotein.
• Proteolytic cleavage of polyprotein precursors to yield actual viral proteins.

Question 9

Chronic leukemia viruses (3):

Answer 9

• In vitro: no transformation.
• No SRC gene or oncogene.
• In vivo: activate protooncogene that is already present in cell DNA.

Question 10

Acute leukemia viruses (4):

Answer 10

• SRC or other oncogene is present.
• Sarcoma in vivo.
• Usually defective (lack Env gene).
• Require helper virus for replication.

Question 11

Oncogenes:

Answer 11

• Cellular equivalent to viral oncogenes, called proto-oncogenes. c-onc.