Protein kinase CK2 or PKCK2 (formerly known as casein kinase 2) is a serine/threonine kinase, and consists of two constitutively active catalytic (a and a’) and two identical regulatory (b) subunits that form an active tetrameric holozyme. CK2 is involved in an array of cellular responses including cell survival, neoplasia and viral infections, and mediates its survival and anti-apoptotic role in part by protecting cellular proteins from caspase-mediated degradation via their phosphorylation. CK2b (25kD) undergoes phosphorylation at serines 2 and 3 in the Nterminal region and serine 209 in the carboxyl terminus. CK2b serine 209 is phosphorylated by p34cdc2 during mitosis.