Avian sarcoma virus (ASV) is a retrovirus with many similarities to HIV, the virus that causes AIDS (acquired immunodeficiency syndrome). Retroviruses code for at least three enzymes: protease (PR), reverse transcriptase (RT), and integrase (IN). Proteases are found in all organisms, from bacteria to humans. Reverse transcriptase and integrase are mainly used by retroviruses and not found in the normal host cell "house keeping" functions. For this reason, it is hoped that drugs that are effective and specific in blocking RT or IN may have few side effects. Preliminary reports about anti-RT drugs in clinical trials give positive results.

Although there are several approved drugs that work against PR and RT, and more anti-PR and anti-RT drugs are undergoing preclinical and clinical trials, no drugs have yet been developed against IN. One reason is that, until recently, little three-dimensional (3D) structural information was known about this enzyme, so the search for anti-IN drugs was a fairly random process. Thus, progress has been slow. By giving synthetic chemists (i.e. drug designers) structural information, we can help them visualize how drugs interact with IN. We can also help them evaluate how well specific candidate drugs target important elements of the IN molecule. This is called "rational" or "structure based" drug design; it can speed drug development by providing details on drug- enzyme contacts, pinpointing specific chemical groups, or even specific atoms, for modification. PR was the first retroviral enzyme targeted by drug designers; RT was the second. (The anti-RT drug AZT was first developed to fight cancer.) IN is the latest retroviral enzyme targeted for rational drug design. We hope structural information about IN, as a part of rational drug design studies, will lead to the development of the next generation of anti-retroviral drugs.