Analysis of interactions between the subunits of protein kinase CK2

Protein kinase CK2, which was formerly known as casein kinase II, is a highly conserved protein serine/threonine kinase implicated in the control of cell proliferation through its phosphorylation of regulatory nuclear proteins. The enzyme consists of catalytic (α and (or) α′) subunits and β subunits that modulate the activity of the catalytic subunits. These subunits are arranged in homotetrameric (i.e., α2β2 or α′2β2) or heterotetrameric (i.e., αα′β2) complexes. We previously demonstrated using the yeast two-hybrid system that α (or α′) subunits can interact with β subunits but not other α (or α′) subunits. By comparison, β subunits can interact with α (or α′) and with β subunits, suggesting that the protein kinase CK2 holoenzyme forms because of the ability of p subunits to dimerize, bringing two heterodimers (αβ or α′β) into a tetrameric complex. In the present study, we used the yeast two-hybrid system to examine the domains of interactions between the α and β subunits of protein kinase CK2. These studies indicate that the ability of β to interact with α resides within the carboxy-terminal domain of β. By comparison, our studies suggest that individual domains of α are not sufficient for interactions with β.Key words: protein kinase CK2, casein kinase II, yeast two-hybrid system, subunit interaction, signal transduction.