Human Retroviruses

Question 1

What are HERVs?

Answer 1

Human endogenous retroviruses (ancient retroviruses that have integrated into germ line cells)

Most are defective and cannot produce virus.

Question 2

The gag-pol precursor ultimately produces ___________.

Answer 2

integrase and reverse transcriptase

Question 3

What are LTRs?

Answer 3

Long terminal repeats –pieces of repeat DNA at the ends of HIV genes required for viral splicing and activation of transcriptase

Question 4

Where (in the cell) does reverse transcriptase act?

Answer 4

In the cytoplasm

Once the ssRNA has been converted to dsDNA, an enzyme shuttles it into the nucleus where it will get spliced into the human genome by integrase.

Question 5

_________ binds to CD4 (specifically CCR5 and CXCR4).

Answer 5

gp120

Question 6

What is the most error-prone step of HIV infection?

Answer 6

Reverse transcription

Question 7

There are three AIDS-defining cancers: ________________.

Answer 7

Kaposi’s sarcoma, cervical cancer, and non-Hodgkin’s lymphoma

Question 8

____________ cancers are on the rise.

Answer 8

Non-AIDS-defining

Question 9

The first retrovirus linked to human disease was _______________.

Answer 9

human T-lymphotropic virus

Question 10

What diseases does HTLV cause?

Answer 10

• Adult T-cell leukemia/lymphoma
• Uveitis
• Myelopathy

Question 11

Describe the structure of HIV.

Answer 11

It is an enveloped virus with a protein capsid and two separate strands of positive-sense ssRNA.

Question 12

Describe the process by which HIV infects host cells.

Answer 12

1) gp120 binds to CCR5 and CXCR4 and sticks gp41 into the host cell membrane
2) The lipid envelope dissolves into the host membrane
3) The protein capsid dissolves
4) Reverse transcriptase converts the ssRNA genome of HIV into DNA:RNA
5) Ribonuclease degrades the RNA and replaces it with DNA, leaving DNA:DNA
6) Integrase brings the DNA:DNA HIV into the nucleus and splices it into the host genome
7) Host RNA polymerase II writes viral mRNA to create new virions

Question 13

HIV pol encodes __________.

Answer 13

protease and integrase

Question 14

Splicing is only required for one of the HIV gene groups: _____________.

Answer 14

env (meaning gag and pol do not require splicing)

Think about a envelope opener slicing open a letter.

Question 15

The LTRs contain ________________.

Answer 15

promoter elements

Question 16

The most common mechanism of viral oncogenesis is ____________.

Answer 16

viral genes up-regulating cellular oncogenes

Question 17

What causes most of the AIDS-associated cancers (both defining and non-defining)?

Answer 17

Other viruses! Think about it: Kaposi’s is caused by HHV-8; anal cancer is caused by HPV; and non-Hodgkin’s lymphoma is caused by EBV.

Question 18

How is HTLV transmitted?

Answer 18

Only through contact with infected cells: IV drug use; mother-to-child; sexual.

Question 19

Describe HAM.

Answer 19

HTLV-Associated Myelopathy (also called tropical spastic paraparesis) is a demyelinating disorder of the spinal cord that results from infection with HTLV. It is rarely fatal.

It can resemble MS.

Question 20

The gag precursor leads to __________.

Answer 20

capsid and matrix

Question 21

The pol precursor leads to ____________.

Answer 21

reverse transcriptase, integrase, and protease

Question 22

What viral gene acts to express HIV once it’s in the host genome?

Answer 22

tat

Question 23

_____________ is required for virion release.

Answer 23

Vpu

Question 24

In general cancers caused by HIV or other retroviruses are _______________.

Answer 24

more aggressive, more likely to present in a young person, and more likely to relapse

Question 25

HTLV causes three known disease phenotypes: _______________.

Answer 25

• ATLL
• Uveitis
• HAM