Cry4

Cry4 is a gene that encodes a protein belonging to the cryptochrome family. Cryptochromes are a class of blue light receptors found in plants and animals, playing crucial roles in circadian rhythm regulation, photomorphogenesis, and DNA repair. In *Drosophila melanogaster*, the fruit fly, the cryptochrome gene has been studied extensively, and Cry4 represents one of the four identified cryptochromes within this organism.

The Cry4 protein, like other cryptochromes, contains a photolyase homology region (PHR) and a C-terminal extension. The PHR domain is responsible for binding flavin adenine dinucleotide (FAD), a cofactor that absorbs blue light. Upon light absorption, FAD undergoes a photochemical reaction, which in turn triggers a conformational change in the protein. This change allows cryptochromes to interact with other proteins, thereby transducing the light signal into cellular responses.

Research on Cry4 in *Drosophila* has suggested its involvement in various physiological processes, although its specific functions are still being elucidated. It is believed to contribute to the synchronization of the internal biological clock with the external light-dark cycle. Studies have explored its potential roles in sleep regulation, reproductive timing, and even flight behavior. The precise mechanisms by which Cry4 exerts its influence and its interactions with other circadian clock components are areas of ongoing scientific investigation. Understanding Cry4's function contributes to a broader understanding of how light influences biological systems.