Orphan receptor involved in normal circadian rhythm behavior (PubMed:26882873). Acts through the G-protein subclass G(z)-alpha and has an agonist-independent basal activity to repress cAMP production (PubMed:26882873). Expressed mainly in the brain, with prominent expression in the SCN (at protein level) (PubMed:26882873). Fluctuates in a circadian fashion, with highest level in night and lowest in the morning (at protein level). Deficient mice exhibit a significantly shorter circadian period. Belongs to the G-protein coupled receptor 1 family.