Protein Kinase Casein Kinase 2 (PKCK-2) is a ubiquitous Ser/Thr kinase expressed in all eukaryotes. It phosphorylates a number of proteins involved in various cellular processes. PKCK-2 holoenzyme is catalytically active tetramer, composed of two homologous or identical and constitutively active catalytic (α) and two identical regulatory (β) subunits.