Structural analysis, expression, and chromosomal localization of the mouse ikba gene

The pleiotropic transcription factor NF-kappa KB is localized in the cytoplasm bound to its inhibitory subunit I kappa B. The predominant form of NF-KB is a p50/p65 heterodimer which can be released from I kappa B-alpha and migrate to the nucleus. Previous studies have shown that I kappa B-alpha(-/-) mice die 8 to 10 days postnatally, showing runting and a severe dermatitis. However, the organ distribution of mouse I kappa B-alpha, the exon-intron structure, and the chromosomal localization of ikba have not been determined so far. A mouse Sv129 genomic DNA library was screened with a human I kappa B-alpha/MAD-3 cDNA probe. One clone (P1) was isolated, spanning the complete ikba gene and the promoter/enhancer region. We show that the exon-intron structure between mouse and pig ikba is completely conserved. In contrast to human ikba, the ankyrin repeat 5 is not interrupted by an intron. Furthermore, the mouse ikba promoter contains 6 putative NF-kappa B binding sequences, which are conserved in mouse, pig, and human, underlining the importance of NF-kappa B as a key regulator of ikba transcription. The deduced amino acid sequence shows >90% similarity between mouse, pig, and human ikba. Chromosome mapping localized the mouse ikba gene to chromosome 12. Northern blot analysis demonstrated predominant expression in lymphoid tissue (lymph node and thymus). However, I kappa B-alpha mRNA was detected as well in liver tissue, the gastrointestinal tract, and the reproductive tract. The cloning and determination of the structure are a prerequisite for the construction of vectors for conditional gene targeting experiments.