Cell
Volume 91, Issue 2, 17 October 1997, Pages 243-252
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Article
The IκB Kinase Complex (IKK) Contains Two Kinase Subunits, IKKα and IKKβ, Necessary for IκB Phosphorylation and NF-κB Activation

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Abstract

Recently we purified a 900 kDa cytokine-responsive IκB kinase complex (IKK) and molecularly cloned one of its subunits, IKKα, a serine kinase. We now describe the molecular cloning and characterization of IKKβ, a second subunit of the IKK complex. IKKβ is 50% identical to IKKα and like it contains a kinase domain, a leucine zipper, and a helix-loop-helix. Although IKKα and IKKβ can undergo homotypic interaction, they also interact with each other and the functional IKK complex contains both subunits. The catalytic activities of both IKKα and IKKβ make essential contributions to IκB phosphorylation and NF-κB activation. While the interactions between IKKα and IKKβ may be mediated through their leucine zipper motifs, their helix-loop-helix motifs may be involved in interactions with essential regulatory subunits.

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