In vivo functional significance of direct physical interaction between Period and Cryptochrome in mammalian circadian rhythm generation.

In the current model, the auto-negative feedback action of Period (Per) and Cryptochrome (Cry) on their own transcription is the hallmark mechanism driving cell-autonomous circadian rhythms. Although this model likely makes sense even if Per and Cry undertake this action in a mutually independent manner, many studies have suggested the functional significance of direct physical interaction between Per and Cry. However, even though the interaction is a biochemical process that pertains to the fundamentals of the circadian oscillator, its in vivo contribution to circadian rhythm generation remains undefined.