Interaction of the β subunit of casein kinase II with the ribosomal protein L5

Abstract

Casein kinase II (CKII) usually exists as a heterotetramer with α2β2, αα'β2, or α'2β2. The α or α' subunits catalyze protein phosphorylation, whereas the function of the β subunit remains unclear. One of the possible functions of the β subunit may be to mediate the interaction of the catalytic subunit with target proteins. To identify proteins capable of associating with the β subunit in vivo, we have used a two-hybrid system. One protein identified is human ribosomal protein L5. The protein L5 does not interact with the α or α' subunits of CKII, supporting the idea that the β subunit can determine a substrate specificity of CKII. These results furthermore suggest a novel role for CKII in ribosomal L5 phosphorylation, in ribosomal assembly, or ribosomal transport in the intact cells. The protein L5 may act as a regulator of the activity or subcellular localization of CKII.