INTERACTION OF THE BETA-SUBUNIT OF CASEIN KINASE-II WITH THE RIBOSOMAL-PROTEIN L5

Casein kinase II (CKII) usually exists as a heterotetramer with alpha( 2) beta(2), alpha alpha'beta(2), or alpha(2)'beta(2). The alpha or alp ha' subunits catalyze protein phosphorylation, whereas the function of the beta subunit remains unclear. One of the possible functions of th e beta subunit may be to mediate the interaction of the catalytic subu nit with target proteins. To identify proteins capable of associating with the beta subunit in vivo, we have used a two-hybrid system. One p rotein identified is human ribosomal protein L5. The protein L5 does n ot interact with the alpha or alpha' subunits of CKII, supporting the idea that the beta subunit can determine a substrate specificity of CK II. These results furthermore suggest a novel role for CKII in ribosom al L5 phosphorylation, in ribosomal assembly, or ribosomal transport i n the intact cells. The protein L5 may act as a regulator of the activ ity or subcellular localization of CKII. (C) 1996 Academic Press, Inc.