Period Circadian Protein 2 (PER2)

PER2 is a member of the Period family of genes and is expressed in a circadian pattern in the suprachiasmatic nucleus, the primary circadian pacemaker in the mammalian brain. Genes in this family encode components of the circadian rhythms of locomotor activity, metabolism, and behavior. Circadian expression in the suprachiasmatic nucleus continues in constant darkness, and a shift in the light/dark cycle evokes a proportional shift of gene expression in the suprachiasmatic nucleus. The specific function of this gene is not yet known.

A new genetic test from a cheek swab can use Per2 expression levels to tell whether a person is an early morning person or a "night owl". It has also been shown that Per2 and Bmal1 work in opposition to each other.