The following amino acids of the Xenopus laevis β subunit of protein kinase CK2 (casein kinase 2) were changed to alanine: Pro-58 (β P→A); Asp-59 and Glu-60 and Glu-61 (β DEE→AAA); His-151–153 (β HHH→AAA). The last 37 amino acids of the carboxyl end were deleted (β Δ179–215). Stimulation of CK2α catalytic subunit activity was measured with casein as substrate and the following relative activities were observed: β P→A > β DEE→AAA ⪢ β WT > β HHH→AAA ⪢ β Δ179–215. The β DEE→AAA and β P→A were similar to β WT in reducing CK2α binding to DNA but β Δ179–215 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.
