Human Retroviruses Flashcards
What are HERVs?
Human endogenous retroviruses (ancient retroviruses that have integrated into germ line cells)
Most are defective and cannot produce virus.
The gag-pol precursor ultimately produces ___________.
integrase and reverse transcriptase
What are LTRs?
Long terminal repeats –pieces of repeat DNA at the ends of HIV genes required for viral splicing and activation of transcriptase
Where (in the cell) does reverse transcriptase act?
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.
_________ binds to CD4 (specifically CCR5 and CXCR4).
gp120
What is the most error-prone step of HIV infection?
Reverse transcription
There are three AIDS-defining cancers: ________________.
Kaposi’s sarcoma, cervical cancer, and non-Hodgkin’s lymphoma
____________ cancers are on the rise.
Non-AIDS-defining
The first retrovirus linked to human disease was _______________.
human T-lymphotropic virus
What diseases does HTLV cause?
- Adult T-cell leukemia/lymphoma
- Uveitis
- Myelopathy
Describe the structure of HIV.
It is an enveloped virus with a protein capsid and two separate strands of positive-sense ssRNA.
Describe the process by which HIV infects host cells.
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
HIV pol encodes __________.
protease and integrase
Splicing is only required for one of the HIV gene groups: _____________.
env (meaning gag and pol do not require splicing)
Think about a envelope opener slicing open a letter.
The LTRs contain ________________.
promoter elements
The most common mechanism of viral oncogenesis is ____________.
viral genes up-regulating cellular oncogenes
What causes most of the AIDS-associated cancers (both defining and non-defining)?
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.
How is HTLV transmitted?
Only through contact with infected cells: IV drug use; mother-to-child; sexual.
Describe HAM.
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.
The gag precursor leads to __________.
capsid and matrix
The pol precursor leads to ____________.
reverse transcriptase, integrase, and protease
What viral gene acts to express HIV once it’s in the host genome?
tat
_____________ is required for virion release.
Vpu
In general cancers caused by HIV or other retroviruses are _______________.
more aggressive, more likely to present in a young person, and more likely to relapse
HTLV causes three known disease phenotypes: _______________.
- ATLL
- Uveitis
- HAM
