CK1δ is a member of the CK1 family of serine/threonine protein kinases which play an important role in diverse cell processes, including DNA replication and repair. CK1δ is a regulator of Yes-associated protein (YAP) transcription coactivator which is a key regulator of organ size and a candidate human oncogene. CK1δ is activated by CCK2R and this then phosphorylates PKD2 at Ser244. Phosphorylation of PKD2 leads to its nuclear accumulation and efficient phosphorylation of nuclear PKD2 substrates in human gastric cancer cells (1). CKIδ can phosphorylate in vitro deoxycytidine kinase (dCK) which is a key enzyme in the salvage of deoxynucleosides. Phosphorylation of dCK by CKIδ in vitro correlates with increased activity of this enzyme (2).