CKII is a serine/threonine protein kinase that phosphorylates acidic proteins such as casein. The kinase exists as a tetramer and is composed of an alpha, an alpha prime, and two beta subunits. The alpha subunits contain the catalytic activity while the beta subunits undergo autophosphorylation. The gene for this protein is found on chromosome 20, but a related transcribed pseudogene is found on chromosome 11. Three transcript variants have been found, encoding two different isoforms. Protein kinase CKII is recognized as one of the key cellular signals for cell growth and proliferation; it also has an important role in apoptosis.