1 Department of Molecular, Cell and Developmental Biology, University of California, Los Angeles, 621 Charles Young Drive South, Los Angeles, CA 90095-1606, USA
2 Radiation Biology Center, Kyoto University, Yoshidakonoe-cho, Sakyoku, Kyoto 606-8501, Japan
Genome Biology 2005, 6:220 doi:10.1186/gb-2005-6-5-220Published: 29 April 2005
Cryptochromes are photoreceptors that regulate entrainment by light of the circadian clock in plants and animals. They also act as integral parts of the central circadian oscillator in animal brains and as receptors controlling photomorphogenesis in response to blue or ultraviolet (UV-A) light in plants. Cryptochromes are probably the evolutionary descendents of DNA photolyases, which are light-activated DNA-repair enzymes, and are classified into three groups - plant cryptochromes, animal cryptochromes, and CRY-DASH proteins. Cryptochromes and photolyases have similar three-dimensional structures, characterized by an α/β domain and a helical domain. The structure also includes a chromophore, flavin adenine dinucleotide (FAD). The FAD-access cavity of the helical domain is the catalytic site of photolyases, and it is predicted also to be important in the mechanism of cryptochromes.