Casein kinase II of yeast contains two distinct alpha polypeptides and an unusually large beta subunit

Casein kinase II of yeast has been purified to near homogeneity by a procedure which includes affinity chromatography on heparin-agarose. The purified enzyme consists of four polypeptides with molecular weights of 42,000, 41,000, 35,000, and 32,000. The 42,000- and 35,000-Da polypeptides are immunologically related and exhibit cross-reactivity with the alpha subunits of calf and Drosophila casein kinase II. Amino-terminal sequencing reveals that the two subunits are distinct but homologous polypeptides and that both sequences share 40-50% homology with the Drosophila alpha subunit. These results demonstrate that yeast contains two distinct alpha subunits which must be encoded by separate genes. The 41,000- and 32,000-Da polypeptides both incorporate phosphate during autophosphorylation, a characteristic of the beta subunit in all type II casein kinases studied to date. The 41,000-Da subunit also exhibits immunological cross-reactivity with the beta subunit of Drosophila casein kinase II. These results identify the 41,000-Da polypeptide as an unusually large beta subunit. The possibility that the 32,000-Da polypeptide may be a beta' subunit is currently under investigation. The interpretation of the subunit structure of yeast casein kinase II reported here differs significantly from previous reports (Rigobello, M. P., Jori, E., Carignani, G., and Pinna, L. A. (1982) FEBS Lett. 144, 354-358; Kudlicki, W. N., Szyszka, R., and Gasior, E. (1984) Biochim. Biophys. Acta 784, 102-107).