Characterization of protein interaction among subunits of protein kinase CKII in vivo and in vitro.

Protein kinase CKII (CKII) is a ubiquitous protein serine/threonine kinase. CKII usually exists in tetrameric complexes composed of two catalytic (CKII alpha and/or CKII alpha') and two regulatory (CKII beta) subunits. In the present study, using a combined in vivo and in vitro approach, we have investigated the role of CKII subunits in the formation of the tetrameric structure of CKII and the formation of the polymeric structure of CKII holoenzyme. Our in vivo experiments show that CKII beta interacts with either another CKII beta or CKII alpha and that CKII alpha does not interact with another CKII alpha (or CKII alpha'). Our in vitro experiments also show that CKII beta is able to associate with both CKII alpha and another CKII beta and that CKII alpha exists as a monomeric form in solution. These data indicate that CKII beta mediates the formation of a tetramer by both the dimerization of CKII beta and the interaction of CKII beta with CKII alpha. The results of this study also suggest that CKII beta may be involved in the formation of the polymeric structure of the CKII holoenzyme.