* Cry1 and Cry2 – Cryptochromes are a class of blue light sensitive flavoproteins found in plants and animals. Cry1 and Cry2 code for the proteins CRY1 and CRY2. In Drosophila, CRY1 and CRY2 bind to TIM, a circadian gene that is a component of the transcription-translation negative feedback loop, in a light dependent fashion and blocks its function. In mammals, CRY1 and CRY2 are light independent and function to inhibit the CLOCK-BMAL1 dimer of the circadian clock which regulates cycling of Per1 transcription.
* Bmal1 – Bmal1 also known as ARNTL or Aryl hydrocarbon receptor nuclear translocator-like, encodes a protein that forms a heterodimer with the CLOCK protein. This heterodimer binds to E-box enhancers found in the promoter regions of many genes such as Cry1 and Cry2 and Per1-3, thereby activating transcription. The resulting proteins translocate back into the nucleus and act as negative regulators by interacting with CLOCK and/or BMAL1 inhibiting transcription.
* Clock – Clock, also known as Circadian Locomotor Output Cycles Kaput, is a transcription factor in the circadian pacemaker of mammals. It affects both the persistence and period of circadian rhythms by its interactions with the gene Bmal1. For more information, refer to Bmal1.
* Per genes – There are three different per genes, also known as Period genes, (per 1, per 2, and per 3) that are related by sequence in mice. Transcription levels for mPer1 increase in the late night before subjective dawn and is followed by increases in the levels of mPer3 and then by mPer2. mPer1 peaks at CT 4-6, mPer3 at CT 4 and 8 and mPer2 at CT 8. mPer1 is necessary for phase shifts induced by light or glutamate release. mPer 2 and mPer3 are involved in resetting the circadian clock to environmental light cues.