Interactions of protein kinase CK2 subunits

Several approaches have been used to study the interactions of the subunits of protein kinase CK2. The inactive mutant of CK2 alpha that has Asp 156 m utated to Ala (CK2 alpha A(156)) is able to bind the CK2 beta subunit and t o compete effectively in this binding with wild-type subunits alpha and alp ha'. The interaction between CK2 alpha A(156) and CK2 beta was also demonst rated by transfection of epitope-tagged cDNA constructs into COS-7 cells. I mmunoprecipitation of epitope-tagged CK2 alpha A(156) coprecipitated the be ta subunit and vice-versa. The assay of the CK2 activity of the extracts ob tained from cells transiently transfected with these different subunits yie lded some surprising results: The CK2 specific phosphorylating activity of these cells transfected with the inactive CK2 alpha A(156) was considerably higher than the control cells transfected with vectors alone. Assays of th e immunoprecipitated CK2 alpha A(156) expressed in these cells, however, de monstrated that the mutant was indeed inactive. It can be concluded that tr ansfection of the inactive CK2 alpha A(156) affects the endogenous activity of CK2. Transfection experiments with CK2 alpha and beta subunits and CK2 alpha A(156) were also used to confirm the interaction of CK2 with the gene ral CDK inhibitor p21(WAF1/CIP1) co-transfected into these cells. Finally a search in the SwissProt databank for proteins with properties similar to t hose derived from the amino acid composition of CK2 beta indicated that CK2 beta is related to protein phosphatase 2A and to other phosphatases as wel l as to a subunit of some ion-transport ATPases.