In a search for protein kinase CK2 beta subunit binding proteins using the two-hybrid system, more than 1000 positive clones were isolated. Beside clones for the alpha' and beta subunit of CK2, there were clones coding for a so far unknown protein, whose partial cDNA sequence was already deposited in the EMBL database under the accession numbers R08806 and Z17360, for the ribosomal protein L5 and for A-Raf kinase. All isolated clones except the one for CK2 beta showed no interaction with the catalytic alpha subunit of CK2. A-Raf kinase is a new interesting partner of CK2 beta. The isolated A-Raf clone represented amino acids 268-606, but also a full length A-Raf clone interacted with CK2 beta. At the site of CK2 beta, residue 175 and amino acids between residues 194 and 200 are likely to be involved in direct interaction.