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Interactions between the Subunits of Casein Kinase II (*)

R. Daniel Gietz,K. C. Graham,David W. Litchfield

Published 1995 in Journal of Biological Chemistry

ABSTRACT

Casein kinase II (CKII) is a protein serine/threonine kinase known to control the activity of a variety of regulatory nuclear proteins. This enzyme has a tetrameric structure composed of two catalytic (α and/or α′) subunits and two β subunits. We have examined the subunit composition of tetrameric complexes of purified bovine CKII by immunoprecipitation using α, α′, or β subunit-specific antibodies. These experiments indicate that the enzyme can exist as homotetramers (i.e. α2β2 or α2′β2) as well as heterotetramers (i.e. αα′β2). To further examine subunit interactions between the α, α′, or β subunits of CKII, we have utilized the yeast two-hybrid system (Fields, S. and Song, O.(1989) Nature 340: 245-246). For these studies, each subunit of human CKII was expressed in yeast as a fusion with the DNA binding domain or with the transcriptional activation domain of the yeast GAL4 transcriptional activator. These studies demonstrate that the α or α′ subunits of CKII can interact with the β subunits of CKII, but not with other α or α′ subunits. By comparison, the β subunits of CKII can interact with α, α′, or β subunits. These results indicate that the CKII holoenzyme forms because of the ability of β subunits to dimerize, bringing two heterodimers (αβ or α′β) into a tetrameric complex.

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