CLOCK

Circadian Locomotor Output Cycles Kaput, or Clock is a gene which encodes proteins regulating circadian rhythm. The CLOCK protein seems to affect both the persistence and length of the circadian cycle. CLOCK forms part of a basic-helix-loop-helix transcription factor. BMAL-1 dimerizes with CLOCK in vivo and transactivates gene expression of Period and Timeless in drosophila by binding to E-box elements in their promoters. BMAL1-CLOCK also regulates Cryptochrome genes (e.g. Cry1, Cry2) and Period genes (e.g. Per1, Per2, Per3) in mammals. The BMAL-CLOCK complex itself is regulated by the expression of Per and Cry genes.