"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 clock, which regulates the daily rhythms of locomotor activity, metabolism, and behavior. circadian expression of these genes and their encoded proteins in the suprachiasmatic nucleus. human per2 is involved human sleep disorder and cancer formation. lowered "per2" expression is common in many tumors cells within the body, suggesting per2 is integral for proper function and decreased levels promotes tumor progression.