CASEIN KINASE-II OF SACCHAROMYCES-CEREVISIAE CONTAINS 2 DISTINCT REGULATORY SUBUNIT-BETA AND SUBUNIT-BETA'

The subunit composition of casein kinase II (CKII) from S. cerevisiae has been difficult to define, particularly with respect to the existen ce and number of regulatory (beta) subunits. A single, integral beta s ubunit, a loosely associated beta subunit, two distinct beta subunits, and a complete absence of beta subunits have all been proposed. Our l aboratory reported yeast CKII to be composed of four polypeptides of 4 2, 41, 35, and 32 kDa (R. Padmanabha and C. V. C. Glover, 1987, J. Bio l. Chem. 262, 1829-1835). The 42- 35-kDa polypeptides were identified as distinct catalytic subunits, alpha and alpha', On the basis of N-te rminal sequencing and subsequent molecular cloning. The 41- and 32-kDa polypeptides were found to undergo autophosphorylation, a characteris tic of the beta subunit in other species, but antibodies raised agains t the beta subunit of Drosophila CKII crossreacted only with the 41-kD a polypeptide. In order to clarify the subunit composition of yeast CK II, particularly with regard to the 32-kDa polypeptide, we have purifi ed the enzyme to homogeneity using a modified procedure. Based on the results of autophosphorylation studies, Western blotting, peptide mapp ing of the 41- and 32-kDa polypeptides, and sequencing of subunit-spec ific peptides, we demonstrate that the 32-kDa polypeptide is an additi onal beta subunit (beta') distinct from the 41-kDa beta subunit. This represents the first demonstration of beta subunit heterogeneity in pu rified CKII from any species. (C) 1994 Academic Press, Inc.