SITE-DIRECTED MUTANTS OF THE BETA-SUBUNIT OF PROTEIN-KINASE CK2 DEMONSTRATE THE IMPORTANT ROLE OF PRO-58

The following amino acids of the Xenopus laevis beta subunit of protein kinase CK2 (casein kinase 2) were changed to alanine: Pro-58 (beta(P) (-->) (A); Asp-59 and Glu-60 and Glu-61 (beta(DEE) (-->) (AAA)); His-151-153 (beta(HHH) (-->) (AAA)). The last 37 amino acids of the carboxyl end were deleted (beta(Delta 179-215)). Stimulation of CK2 alpha catalytic subunit activity was measured with casein as substrate and the following relative activities were observed: beta(P) (-->) (A) > beta(DEE) (-->) (AAA) much greater than beta(WT) > beta(HHH) (-->) (AAA) much greater than beta(Delta 179-215.) The beta(DEE) (-->) (AAA) and beta(P) (-->) (A) were similar to beta(WT) in reducing CK2 alpha binding to DNA but beta(Delta 179-215) was less active, The results indicate that both Pro-58 and the surrounding acidic cluster play roles in dampening the activation of CK2 alpha and that the carboxyl end of beta is involved in the interaction with CK2 alpha.