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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