Phosphorylation and destabilization of human period I clock protein by human casein kinase I epsilon

Period (PER), a central component of the circadian clock in Drosophila, und ergoes daily oscillation in abundance and phosphorylation state. Here we re port that human casein kinase I epsilon (hCKI epsilon) can phosphorylate hu man PERI (hPERI). Purified recombinant hCKI epsilon (but not a kinase negat ive mutant of hCKI epsilon, hCKI epsilon-K38R) phosphorylated hPERI in vitr o. When co-transfected with wild-type hCKI epsilon, in 293T cells, hPERI sh owed a significant increase in phosphorylation as evidenced by a shift in m olecular mass. Furthermore, phosphorylation of hPERI by hCKI epsilon caused a decrease in protein stability in hPERI. Whereas phosphorylated hPERI had a half-life of approximately 12 h, unphosphorylated hPERI remained stable in the cell for > 24 h. hPERI protein could also be co-immunoprecipitated w ith transfected hCKI epsilon as well as endogenous hCKI epsilon, indicating physical association between hPERI and hCKI epsilon proteins in vivo. Neur oReport 11:951-955 (C) 2000 Lippincott Williams & Wilkins.