Professor of Chemistry Stuart L. Schreiber is hot.

So hot in fact, that Science Watch magazine has named him the fourth "hottest" scientist in the world for 1993.

The magazine compiles rankings according to its "hot papers database," which keeps track of the most frequently cited research papers.

Schreiber, a chemical cell biologists, has written seven "hot papers" that are being cited heavily by scientists around the world.

Schreiber's breakthrough research included his discover of the mechanism by which certain drugs block the action of key enzymes in the human immune system.

Schreiber investigated one of these so-called immunosuppressants in particular, FK506, which was obtained from soil samples. He found that it acts as a inhibitor and causes the immune system to lose function.

Schreiber says of this work, FK506 taught us a lot about signal transduction--the way in which cells received signals and translate them into action."

One of the most important clinical applications of FK506 lies in organ transplants.

When a patient undergoes a transplant, there is a risk of the body rejection the new organ. Drugs like FK506 suppress the immune system's inclination to act against, and possibly reject, the new organ.

"The immune system can sense the presence of a virus, and can act by dispatching cells to attack the virus," Schreiber says.

A post doctoral fellow in Schreiber's lab says the professor's work has been highly original and creative.

He says that the potential clinical applications of FK506 could be very important because it has fewer side effects and can be administered in much smaller concentrations than the immunosuppressants currently in use.

Schreiber is currently investigating other natural products that interfere with chemical pathways.

"We are making our own tailor made molecules to see pathways, and even to control and regulate them," says Schreiber.

Schreiber says he is excited about the research is conducting and its potential applications.

"It is truly exhilarating," he says. "This is the hey-day for this kind of research in chemistry and biology."

Schreiber was not the only Harvard scientist among the world's hottest researchers.

Dennis J. Selkoe, professor of neurology at Brigham & Women's Hospital, placed fifth on Science Watch's "hot" list. Selkoe has published six "hot papers" dealing with Alzheimer's Disease.

The number one cited scientist in the world, according to Science Watch, is Bert Vogelstein, molecular biologist at Johns Hopkins University who has investigated the activity of a tumor suppressor gene.