CSNK1D/CK1d

Casein kinase 1 delta (CK1δ, gene CSNK1D) is best known as a core circadian timer: it phosphorylates PER1 and PER2 proteins, controlling their stability and the period length of the transcription-translation feedback loop. Human CSNK1D variants that alter PER2 phosphorylation cause familial advanced sleep phase syndrome. Beyond the clock, CK1δ acts in Wnt signaling, p53 regulation, microtubule dynamics and neuronal function, and it is expressed in most tissues with enrichment in brain. Together with its close paralog CK1ε, it defines the δ/ε branch of the CK1 family and is a validated target for circadian and cancer therapeutics.