CLOCK (circadian locomotor output cycles kaput), circadian protein, is present in the Z-disk of the myofilaments and is controlled by cross-bridge cycling. It is involved with glucose and fatty acid metabolism. CLOCK protein binds to BMAL1 (brain and muscle ARNT-like 1) to form heterodimer complex. This binding activity enhances the transcription of target genes such as PER (period circadian clock) and CRY (cryptochrome) genes. Furthermore, PER-CRY complex relocates into the nucleus to suppress the CLOCK/BMAL1 complex activity. Thus, it regulates gene expression in a cyclic manner.
