Two ATP-competitive inhibitors-4,5,6,7-tetrabromo-benzotriazole (TBBt) and 4,5,6,7-tetrabromo-benzimidazole (TBBz) have been shown to decrease activity of CK2 holoenzyme. Surprisingly it occurs that TBBz contrary to TBBt does not inhibit free catalytic subunit CK2alpha'. Both inhibitors are virtually inactive against RAP protein kinase. The above-mentioned protein kinases phosphorylate in vitro a set of acidic ribosomal P-proteins of the 60S ribosomal subunit. Such a modification is one of the mechanisms regulating translational activity of ribosomes in vivo. Application of these two very selective inhibitors allows us to define the role of free catalytic alpha' subunit of CK2 in phosphorylation of ribosomal proteins. It occurs that CK2alpha' but not CK2 holoenzyme is responsible for phosphorylation of P-proteins in vivo. Moreover, elimination of both forms of protein kinase CK2 (hCK2 and CK2alpha') activity in living cells led to dramatic loss of the translational activity of the ribosome. (C) 2003 Elsevier Inc. All rights reserved.