Casein Kinases (CKs), a group of ubiquitous Ser/Thr kinases, regulate a wide range of cellular functions in eukaryotes, including phosphorylation of proteins that are substrates for degradation via the ubiquitin-proteasome system (UPS). Two casein kinases, casein kinase-1 (CK-1) and casein kinase-2 (CK-2), have been characterized from many sources.
CK1 kinases exist in at least seven isoforms (α, β, γ1-3, δ, and ɛ) in mammals and CK1 kinases phosphorylate various substrates to play vital roles in diverse physiological processes such as DNA repair, cell cycle progression, cytokinesis, differentiation, and apoptosis. Casein kinase 2 (CK2) is a highly pleiotropic serine-threonine kinase, which catalyzed phosphorylation of more than 300 proteins that are implicated in regulation of many cellular functions, such as signal transduction, transcriptional control, apoptosis, and the cell cycle.