HIV enzyme being affected by a drug. Molecular model of HIV's reverse transcriptase enzyme as it interacts with a drug (not seen). The drug affects the shape and function of the enzyme, thus helping to prevent HIV (the human immunodeficiency virus) causing AIDS (acquired immune deficiency syndrome). The model shows the helices and arrowed sheets representing the enzyme's shape (secondary structure). Reverse transcriptase is an enzyme that is a key part of the process where HIV's RNA (ribonucleic acid) strands are copied for later insertion into the DNA (deoxyribonucleic acid) of the cell being infected. This process is called reverse transcription. This enzyme is from the HIV-1 form of HIV. The drug used here is Emivirine (MKC-442).