cry2 Background Information Cryptochromes are mammalian circadian photoreceptors that absorb light and transmit the electromagnetic signal to the molecular clock using cofactors such as pterin and FAD (flavid adeninedinucleotide) (1,2). CRY1 and CRY2 are evolutionarily conserved cryptochromes (2,5) that are similar to other members of the photolyase/blue-light photoreceptor family (4). CRY1 and CRY2 display 73% amino acid identity (4) and function as light-independent inhibitors of CLOCK-BMAL (3), a heterodimer that regulates circadian rhythm (6). Both human and mouse CRY1 and CRY2 are differentially expressed in the retina relative to the
opsin-based visual photoreceptors (2). CRY1 localizes to the mitochondria, whereas CRY2 localizes to the nucleus (7).
