DNA INHIBITS THE CATALYTIC ACTIVITY OF THE ALPHA-SUBUNIT OF PROTEIN-KINASE CK2

The recombinant alpha subunit of protein kinase CK2 (casein kinase 2) from Xenopus laevis is inhibited by the addition of single stranded or double stranded DNA. This inhibition is competitive with the casein s ubstrate, having an apparent Ki of 160 nM for an 86 bp DNA fragment. A ssays with a fragment containing the putative promoter of the human CK 2 beta gene indicated that the affinity of CK2 for this fragment was n ot greater than that of other unrelated DNA. The inhibitory capacity o f DNA toward the protein phosphorylating activity of CK2 alpha is grea tly reduced by the presence of the beta subunit which can completely r everse the inhibition, The interaction of CK2 alpha with DNA can also be assayed by the nitrocellulose filter binding assay. This assay demo nstrates that the interaction of CK2 alpha with the tested DNAs is not sequence specific and that the beta subunit can also greatly diminish the binding of CK2 alpha to DNA. Casein at substrate concentrations a lso is inhibitory to CK2 alpha DNA binding, Likewise, polyanionic inhi bitors of the CK2 catalytic activity, such as heparin, poly(U), and co poly(alu:Tyr) polypeptides, can compete for and inhibit the binding of DNA to CK2 alpha. However, quercetin, which also inhibits CK2 phospho rylation activity, and ATP do not affect DNA binding. A mutant CK2 alp ha in which glutamic acids replace two lysine residues in positions 75 and 76 of the alpha peptide chain is less susceptible to DNA inhibiti on, indicating that this basic region of the molecule is involved in i ts interaction with DNA.