Mapping of the interaction domain of the protein kinase CKII beta subunit with target proteins

Protein kinase CKII is composed of two catalytic (alpha or alpha') subunits and two regulatory (beta) subunits. The CKII beta subunit is thought to me diate the tetramer formation and interact with other target proteins. Previ ously we have shown that CKII beta interacts with ribosomal proteins L5 and L41, DNA topoisomerase lip, and SAG/CKBBP (1) over tilde. In this study, t he two-hybrid system was used to define the subregions of CKII beta that ar e involved in the interaction with L5, L41, topoisomerase II beta, SAG/CKBB P1, and unknown proteins, CKBBP2 and CKBBP3. The results indicated that the region between residues I and 167 of CKII beta is common binding site for L5, topoisomerase II beta, SAG/CKBBP1, and L41. The region between amino ac ids 19 and 167 of CKII beta is sufficient for the interaction with CKBBP3. The region between residues 67 and 130 of CKII beta is a minimal fragment t hat is required for interaction with CKBBP2. Overlay experiments showed tha t the region between residues 1 and 167 of CKII beta interacts with L5, L41 , and SAG/CKBBP1 in vitro. These results suggest that the binding sites of CKII beta for these target proteins are not located within a small linear s equence stretch, but rather are created by a three-dimensional structure.