Circadian clocks regulate the timing of biological functions in almost all higher organisms. Anyone who has flown through several time zones knows the jet lag that can result when this timing is disrupted.

Now, new research by Cornell and Dartmouth researchers explains the biological mechanism behind how circadian clocks sense light through a process that transfers energy from light to chemical reactions in cells. The research is published in the May 18 issue of the journal Science.

Circadian clocks in cells respond to differences in light between night and day and thereby allow organisms to anticipate changes in the environment by pacing their metabolism to this daily cycle. The clocks play a role in many processes: timing when blooming plants open their petals in the morning and close them at night; or setting when fungi release spores to maximize their reproductive success. In humans, the clocks are responsible for why we get sleepy at night and wake in the morning, and they control many major regulatory functions. Disruptions of circadian rhythms can cause jet lag, mental illness and even some forms of cancer.

"These clocks are highly conserved in all organisms, and in organisms separated by hundreds of millions of years of evolution," said Brian Crane, the paper's senior author and an associate professor in Cornell's Department of Chemistry and Chemical Biology.

The study revealed how a fungus (Neurospora crassa) uses circadian clock light sensors to control production of carotenoids, which protect against damage from the sun's ultraviolet radiation just after sunrise. The researchers studied a protein called vivid, which contains a chromophore -- a light-absorbing molecule. The chromophore captures a photon or particle of light, and the captured energy from the light triggers a series of interactions that ultimately lead to conformational changes on the surface of the vivid protein. These structural changes on the protein's surfac
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Contact: Blaine Friedlander
bpf2@cornell.edu
607-254-8093
Cornell University News Service
22-May-2007