Genes control to a great extent how long an organism can live. For example, researchers have known for a while that adding an extra copy of a gene called SIR2 to a yeast cell lengthens its lifetime. Now they have found that the equivalent gene in worms works the same way: worms with an additional copy of sir-2.1 live up to 50 percent longer than their wild cousins.

Heidi Tissenbaum and Leonard Guarente, who publish their findings in today¿s Nature, also present some clues as to how sir-2.1 might extend a worm¿s lifetime. In the worm's cells, its product interferes with a chain of signals, which are triggered by an insulin-like hormone and might tell the cell whether, say, nutrients are available. The result did not come as a total surprise because other worm genes that play a role in aging¿such as daf-2¿are part of the same signaling cascade. Like SIR2 in yeast, sir-2.1 may exert its effect by shutting down a number of other genes.

The big question now is whetherSIR2-like genes also regulate the rate of aging in humans. It might turn out that the very same gene determines how often a simple yeast cell divides¿and how long a human being can live.