A protein that helps control the motion of the human gut may also help the body keep time with the brain's biological clock, researchers say.

The hunt for a way to prevent jet lag and other sleep disorders has led to a better understanding of how an internal clock in the brain sets the 24-hour cycle of body activities like sleep and wakefulness, called the circadian rhythm.

But the way that clock signals the rest of the body to follow the daily cycle has eluded researchers.

A study in the May 23 issue of the journal Nature implicates a protein called "prokineticin 2" or PK2, which was previously known to help regulate gastrointestinal movements.

Researchers found PK2 had many features scientists would expect in a chemical messenger from the clock, said Qun-Yong Zhou, the University of California-Irvine pharmacologist who led the study.

For example, areas of the brain that control various body functions contain specialized receptors that PK2 can bind to to deliver a signal, Zhou said.

"It certainly looks like receptors are in the right place," said Joseph Takahashi, a Howard Hughes Medical Institute researcher at Northwestern University who cloned a gene in 1997 that helps regulate the circadian rhythm.

Takahashi said the PK2 protein likely is not the only brain clock messenger, but it will offer clues to others that control body functions during the daily cycle.

He said it was too early to say whether it could lead to drugs to ease jet lag or other sleep disorders, but "we're coming closer to that."

The study examined the behavior of rats injected with the protein.

Rats normally are nocturnal, or active during darkness. But when PK2 was injected into the brains of the rats during darkness, they stopped exercising and moving about their cages, adopting behavior more appropriate for daylight.

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