Note: this site last updated in 2006
An article from "The Molecules of HIV" (c) Dan Stowell
Integrase is HIV's enzyme for inserting the DNA version of its genome into the host cell's DNA. It catalyses the "cut-and-paste" operation of snipping the host DNA and attaching the proviral genome to the snipped ends.
There are three "domains" in this protein, in this order:
Integrase carries out a function which is pretty much unique to retroviruses - human cells don't have any need to cut-and-paste bits of DNA into their genome. This means that the inhibition of integrase should be a good target for drug therapy, since it's not likely to interfere with the normal operation of human cells.
The answer is simply that no integrase-inhibitor drug has yet made it through the various testing stages and been approved for clinical use. Some showed promise in test-tube experiments but didn't seem to work in a real living organism. Others show more promise, but have yet to pass through the clinical trial stages that are necessary before any drug can be approved for clinical use.
One type of integrase inhibitor which is currently being looked into is the diketo acids.