This is a very
intricate topic that will most like
bore the
bejeezus out of most people. This is intended to be a general reference addition, like Websters. If links don't work yet, I will be filling them in eventually. If you can fill one in yourself (in reasonable detail), do so! I am trying to include all I can remember, but I am bound to leave
something out, so if I do, tell me! Consider this to be a work in progress, it will be updated as I find mistakes or new research comes to light. This is pretty difficult to do without
pictures, but here goes nothing...
HIV is the virus generally accepted to cause
AIDS. It is an
enveloped
virus, meaning it has a
membrane surrounding it, which is
derived from the
membrane of a
host cell, with additional viral
proteins added (the most important of which are
gp120 and
gp41). Examples of other enveloped species are
Influenza and
herpesvirus. The other major type of
virion is
naked, where there is simply a
protein coat surrounding the virus. They include
picornaviruses and
bacteriophages, among others.
HIV is also a
retrovirus. This means that it has a single
stranded
RNA genome that is converted to a double stranded
cDNA by
reverse transcriptase. This DNA is then
imported to the
nucleus and incorporated into the host genome at a region of active
transcription by the
enzyme integrase. It should be noted that integrase is a fairly unique enzyme, nothing like it exists in humans. It is therefore a very promising target for
antiviral therapy. The integrated viral DNA is known now as a
provirus. It contains a promoter and 3 important genes, known as
gag,
pol, and
env, as well as a variety of
accessory genes that won't be dealt with here.
These genes are transcribed in one long string, and the resulting
RNAs are rearranged to form the
mRNAs for the accessory genes, which
translocate unspliced viral
RNA to the cytoplasm, where they are translated as one long gag-pol
polyprotein by a process that involves
ribosomal frameshifting. The gag-pol polyprotein is cleaved by the viral
protease into smaller structural proteins (viral
matrix,
capsid, and
nucleocapsid proteins], as well as the viral enzymes (
protease,
integrase, and
reverse transcriptase). The viral surface proteins
gp120 and
gp41 are produced as the
gp160 polyprotein, and then cleaved by
cellular proteases. Other accessory proteins regulate the combination of nucleocapsid proteins and viral RNA. This then buds off from the cytoplasm of the cell as a mature virion.
Mature HIV virions infect
CD4+
T-helper cells. They bind when the viral envelope protein
gp120 associates with the
CD4 receptor.
Gp41 then mediates the fusion of the viral envelope with the cell membrane, and the virion enters the cell, thus beginning the cycle over again.
See also:
AZT,
protease inhibitor