Site-directed mutants of the β subunit of protein kinase CK2 demonstrate the important role of Pro-58

The following amino acids of the Xenopus laevis β subunit of protein kinase CK2 (casein kinase 2) were changed to alanine: Pro-58 (βP→A); Asp-59 and Glu-60 and Glu-61 (βDEE→AAA); His-151-153 (βHHH→AAA). The last 37 amino acids of the carboxyl end were deleted (βΔ179-215). Stimulation of CK2α catalytic subunit activity was measured with casein as substrate and the following relative activities were observed: βP→A > βDEE→AAA ≫ βWT > βHHH→AAA ≫ βΔ179-215. The βDEE→AAA and βP→A were similar to βWT in reducing CK2α binding to DNA but βΔ179-215 was less active. The results indicate that both Pro-58 and the surrounding acidic cluster play roles in dampening the activation of CK2α and that the carboxyl end of β is involved in the interaction with CK2α. © 1995