IkappaB kinase-alpha and -beta genes are coexpressed in adult and embryonic tissues but localized to different human chromosomes

Activation of the transcription factor nuclear factor kappa B (NF-kappaB) is regulated by phosphorylation, ubiquitination, and degradation of its inhibitory factor IkappaB. Very recently, two closely related serine/threonine kinases have been identified as IkappaB kinases which are essential for IkappaB phosphorylation and NF-kappaB activation. Here, we isolated the full-length human cDNA clones encoding these two IkappaB kinases, IKK-alpha and IKK-beta. Both polypeptides contain a conserved amino-terminal kinase domain, a leucine zipper motif and a helix-loop-helix domain at their carboxyl terminus. We showed that IKK-alpha and IKK-beta were coexpressed in most human adult tissues as well as in different developmental stages of mouse embryos, suggesting that they may cooperate in the cells. The IKK-alpha and IKK-beta genes are distinct but evolutionarily conserved. Moreover, the IKK-alpha gene locus was mapped to human chromosome 10q24, whereas the IKK-beta gene locus was localized to human chromosome 8p11.2. These results indicated that both genes are not clustered on the same chromosome; nevertheless, both genes may be still regulated similarly during development and in adult tissues.