CKI epsilon is a member of the casein kinase 1 (CK1) serine/threonine kinase family of proteins. In mammals, there are seven distinct genes that represent the CK1 family: alpha, beta, gamma-1, gamma-2, gamma-3, delta, and epsilon. CKI epsilon phosphorylates a large number of proteins and is involved in pathways involving Wnt and AKT. CKI epsilon has been found to bind and phosphorylate the circadian protein, Period, and the Wnt signaling protein, Dsh. In the Wnt pathway, CKI epsilon activity is required for the full activation of Dsh and downstream signaling effects.