Getting a grip on HIV's crucial enzyme.

The AIDS-causing virus HIV must copy its genetice material -- composed of RNA -- into DNA soon after it infects a cell. To do this, it employes reverse transcriptase, an enzyme that uses RNA as a template for making DNA and then destroys the RNA template. AIDS drugs such as zidovudine (AZT) and didanosine (DDI) work by blocking the action of this enzyme, but HIV can sometimes become resistant to these compounds.

This computer model of the enzyme at work, created using X-ray crystallography data, may help scientists design drugs HIV can't elude. It shows how part of the ribbon-like reverse transcriptase enzyme (top right) interacts with a double helix (bottom) made of one strand of RNA and one strand of DNA. The spheres at right highlight the enzyme's site for digesting the RNA template. The spheres at left depict where another part of the enzyme (not shown) adds to the growing DNA chain. The model was created by two teams of researchers led by Edward Arnold at Rutgers University in Piscataway, N.J., and Stephen H. Hughes at the National Cancer Institute facility in Frederick, Md. They report their finding in the May 7 NATURE.