EXPRESSION AND CHARACTERIZATION OF A RECOMBINANT MAIZE CK-2 ALPHA-SUBUNIT

CKIIB, one of the CK-2 like enzymes which have been isolated from maiz e, has been shown to be a monomeric enzyme that cross-reacts with anti CK-2 alpha specific antibodies suggesting a possible relationship bet ween the two proteins (Dobrowolska et al. (1992) Eur. J. Biochem. 204, 299-303). In order to support the immunological data also by biochemi cal and biophysical experiments the availability of a recombinant CK-2 alpha from maize was a prerequisite. A maize cDNA clone of maize CK-2 alpha was expressed in the bacterial strain BL21 (DE3). The recombina nt protein was purified to homogeneity; its molecular mass on one-dime nsional SDS PAGE was estimated to be 36.5 kDa. The calculated molecula r mass according to the amino acid composition is 39 228 Da (332 amino acids). The recombinant maize CK-2 alpha (rmCK-2 alpha) exhibited mos tly the same properties as the recombinant human CK-2 alpha (rhCK-2 al pha). In several respects it behaved differently from CKTIB, thus supp orting the notion that either CKIIB is encoded by another gene or it u ndergoes extensive posttranscriptional and/or posttranslational altera tions. Three observations in particular disprove any close relatedness between CKIIB and rmCK-2 alpha, namely: (a) the phosphorylation of ca lmodulin by CKIIB is dramatically stimulated by polylysine, whereas po lylysine inhibits rather than stimulating the phosphorylation of calmo dulin by rmCK-2 alpha (and by rhCK-2 alpha). (b) Addition of rhCK-2 be ta has no significant influence on the stimulation of the calmodulin p hosphorylation by CKIIB whereas in the case of rmCK-2 alpha and rhCK-2 alpha addition of rhCK-2 beta is required for optimal stimulation by polylysine. (c) CKIIB does not self-assemble with rhCK-2 beta to form a high molecular mass complex as it is demonstrated for rmCK-2 alpha.