Sensible people know better than to believe in pills that promise perpetual youth. But otherwise sensible biologists are excited about the implications of a newly detected gene that, when altered, can double the life-span of fruit flies.

Earlier research has shown that worms, fruit flies, and rodents live longer on a spartan diet. Geneticist Stephen Helfand and his team at the University of Connecticut Health Center in Farmington suspect that their new longevity gene, dubbed "Indy" for "I'm not dead yet," can lead to production of a protein that renders metabolism less efficient. As a result, the body functions as if the fruit fly were dieting, even though its eating habits are unchanged.

The researchers came upon Indy by accident. In mutant strains of fruit flies produced for a different experiment, Helfand noticed that some lived longer than usual. The scientists determined that fruit flies carrying one good copy and one defective copy of Indy lived the longest, averaging 70 days versus the usual 37--a "quite impressive extension of life-span," notes Judith Campisi, a cell and molecular biologist at Lawrence Berkeley National Laboratory in California.

With two altered copies of the gene, flies live only about 20% longer than the norm, the researchers report in the 15 December issue of Science.

Indy codes for a protein that resembles a membrane protein found in many organisms, from bacteria to mammals, including humans. In mammals, the proteins show up in cells in the digestive tract, placenta, liver, kidney, and brain, where they transport metabolic intermediates across the cell membrane.

In the fruit fly, the gene is active in fat bodies--which function as the liver in insects--as well as the midgut, antennae, and cells called oenocytes, which appear to store glycogen. Helfand suggests that the mutant fruit flies have trouble using or absorbing nutrients, which is "the genetic equivalent of caloric restriction."

The discovery "provides the first clear genetic link between metabolism and the rate of aging," says geneticist Tomas Prolla at the University of Wisconsin, Madison. Another geneticist, Seymour Benzer of the California Institute of Technology in Pasadena, is even more enthusiastic: "This [gene] provides optimism that it may, indeed, be possible to manipulate active life-span beyond the constraints that ordinarily apply in natural evolution."

--ELIZABETH PENNISI