P21(WAF1 CIP1) INTERACTS WITH PROTEIN-KINASE CK2/

p21(WAF1/CIP1) which belongs to a class of regulatory proteins that in teract with cyclin dependent kinases is a potent inhibitor of these ki nases. The inhibition of the cyclin dependent kinases induces an arres t of cells in the G(1) phase of the cell cycle. In addition p21(WAF1/C IP1) associates with PCNA and inhibits DNA replication. Here, we show that p21(WAF1/CIP1) binds to the regulatory beta-subunit of protein ki nase CK2 but not to the catalytic alpha-subunit. Binding of p21(WAF1/C IP1) down regulates the kinase activity of CK2 with respect to the pho sphorylation of the beta-subunit of CK2, casein and the C-terminus of p53. This study demonstrates a new binding partner for the regulatory beta-subunit of protein kinase CK2 which regulates the activity of the holoenzyme.