Casein kinases are a group of ubiquitous Ser/Thr kinases that phosphorylate key regulatory proteins involved in the control of cell differentiation, proliferation, chromosome segregation, circadian rhythms, and metabolic pathways. CK1 family members share a highly conserved kinase domain but differ in their variable N- and C-terminal domains. The C-termini of the CK1 gamma isoforms carry putative palmitoylation sites. CK2 is a tetrameric kinase comprised of two catalytic subunits (CK2 alpha and/or CK2 alphaæ) and two identical regulatory subunits (CK2 beta).