Using X-ray crystallography, researchers have solved the three-dimensional structure of an RNA enzyme that plays a role in the replication of the hepatitis delta virus. It is the only example of an RNA catalyst found in a human pathogen and the second example of a fully visualized RNA enzyme. Jennifer Doudna, Ph.D., professor of molecular biophysics and biochemistry and an investigator with the Howard Hughes Medical Institute (HHMI), led the research. Hepatitis delta, a secondary infection that sometimes occurs in patients with hepatitis B, is a significant problem in developing countries, where it is often fatal. “It is known that this RNA enzyme is essential for replication of the virus,” says Dr. Doudna. “Using our knowledge of its molecular structure, it may be possible to design pharmaceuticals that interfere with its function and stop the progression of the disease.”