The find opens the way to understanding how the body stays in synchrony with night and day and of developing drugs to help those whose internal clocks have gone awry.
Mutations in the gene cause the body's circadian rhythm of sleep and wakefulness to break down. When laboratory mice have two copies of the mutated gene they become alert or sleepy at any time of day or night, like some insomniacs, shift workers or travellers who cross time zones.
The gene in mice occurs in a region of its chromosomes that has an equivalent region in humans. This suggests the gene also serves an essential role in the good time-keeping of our own body clock, according to Joseph Takahashi, professor of neurobiology at Northwestern University in Evanston, Illinois.
Designing drugs to help jet lag and insomniacs with inaccurate body clocks is now possible, he said. 'It's clearly a big step towards that because we now have a tangible gene to search for, whereas before we could only guess at what these genes were,' he said.
The research, published in today's issue of the journal Science, is the first to find a gene in a mammal which is essential for keeping the rhythm of the body clock going.
In humans, researchers have shown that a small piece of tissue deep inside the brain - the suprachiasmic nucleus - controls the hormones that keep the body clock ticking away. The brain uses external cues, notably bright light, to ensure the human body clock is adjusted correctly.