The structure of cryptochromes. A comparison of the structures of the photolyase-related (PHR) regions of (a) Arabidopsis CRY1 and (b) E. coli DNA photolyase. White lines indicate the boundaries of the FAD-access cavity; red and blue represent areas of negative and positive electrostatic potential, respectively. Reproduced with permission from ; copyright 2004 National Academy of Sciences USA. (c) A schematic representation of a typical photolyase/cryptochrome superfamily protein. The parts of the PHR region bound by pterin and FAD are indicated with brackets and the domains are shown below the protein. (d) The overall fold of a CRY-DASH protein (Synechosystis sp. PCC6803 cryptochrome).