per2 has been shown to interact with a kinase called ck1e. ck1e phosphorylates per2 in mammals. in syrian hamster, a mutation called tau has been discovered in the ck1e, which increases phosphorylation of homologous per2 leading to a faster degradation and a shortened period. mutations in hper2 can cause fasps because of a lack of phosphorylation site in the mutated hper2 protein.