CLOCK helps stabilize CYCLE to start the internal clock in fruit flies

CLK binds to and stabilizes CYC in cell culture and in nonclock cells in vivo.

• Circadian clocks operate in approximately 150 brain pacemaker neurons and various peripheral tissues.
• CLK-CYC heterodimers initiate transcription of genes that encode feedback repressors, PERIOD and TIMELESS.
• Ectopic clocks can be induced in nonclock cells by expressing CLK, although CYC expression remains limited to canonical clock cells.
• The blue light photoreceptor CRYPTOCHROME (CRY) is essential for light entrainment and clock function in peripheral tissues.
• Mechanisms governing circadian activator stability may be conserved across all eukaryotes.

Simplified