Enables chromatin binding activity. Acts upstream of or within several processes, including circadian regulation of gene expression; entrainment of circadian clock by photoperiod; and locomotor rhythm. Predicted to be active in cytoplasm and nucleus. Is expressed in heart; liver; muscle; nervous system; and ovary. Human ortholog(s) of this gene implicated in advanced sleep phase syndrome; advanced sleep phase syndrome 1; alcohol dependence; cocaine dependence; and fetal alcohol spectrum disorder. Orthologous to human PER2 (period circadian regulator 2).