English: The figure demonstrates the oscillator genes and proteins involved in the mammalian circadian oscillator. At the core of the SCN clock, the two transcription factors CLK and BMAL1 form heterodimers that are then able to to drive the rhythmic expression of three period genes (mPer1, mPer2, mPer3) and two Cryptochrome genes (mCry1 and mCry2) via ebox enhancer elements. The expression of these genes leads to the formation of PER:CRY complexes that are then able to prevent further transcription of mPer and mCry genes by inhibiting the CLOCK:BMAL1 complex. CLOCK:BMAL1 hetrodimers also drive the rhythmic expression of two nuclear orphan receptor genes Rev-erbα and Rora again via ebox enhancer elements. The REV-ERBα and RORa proteins that are consequently produced then compete for the same retinoic acid-related orphan receptor response elements (ROREs) to produce inhibition and promotion of Bmal1 transcription respectively