CHAPEL HILL, NC -- Researchers at the University of North Carolina at Chapel Hill School of Medicine have discovered the proteins which help set the body's daily clock. In an article appearing today (May 26) in the Proceedings of the National Academy of Sciences, Dr. Aziz Sancar, professor of biochemistry, and Dr. Yasuhide Miyamoto, postdoctoral research associate, describe two proteins called cryptochrome (CRY) 1 and 2 which were found in almost all body cells studied. CRY 1 is found in large amounts in a part of the brain known to control daily, or circadian, rhythms.
Dr. Sancar's lab didn't originally set out to find proteins controlling circadian rhythms. The project began when researchers working on the human genome project found an unexpected gene. This gene proved similar to a gene that encodes photolyase, an enzyme involved in repairing DNA damaged by ultraviolet light. Photolayse is found in many organisms, Sancar said, "but I knew for a fact that humans did not have it." Intrigued, Sancar and Miyamoto began studying the genes and the proteins they encode.
Among the places they found CRY 1 and CRY 2 were in layers of the retina which are not involved in forming visual images. There are retinal diseases in humans and mice which destroy the image-forming layers of the retina but leave the rest unharmed. Even though victims of these diseases are blind and cannot see daylight, they still wake up in the morning and go to sleep at night the same as the sighted. Dr. Sancar believes this happens because of the presence of CRY 1 and 2, both in their retinas, and in other cells elsewhere in the body. For example, he said, because CRY1 and 2 were found in the skin, they could be helping set the daily clock from sites in skin cells. This idea agrees with a recent study which showed circadian rhythms can be set by shining light behind the knees.
CRY 1 and 2, which respond to the blue-white region of the sunlight spectrum, are only the second set of light-reactive proteins found in humans in more than 120 years. The other protein, rhodopsin, which is found in the rods and cones of the eye and controls vision, was discovered in 1877.
Journal
Proceedings of the National Academy of Sciences