STRUCTURE AND REGULATION OF THE GENE ENCODING AVIAN INHIBITOR OF NUCLEAR FACTOR KAPPA-B-ALPHA

The Rel/NF-kappa B family of transcription factors exist in the cytopl asm as inactive complexes in association with an inhibitory protein ca lled I kappa B-alpha. We have isolated a clone containing the avian I kappa B-alpha gene from a chicken genomic library. Avian I kappa B-alp ha is devoid of any recognizable promoter elements, i.e., TATA and CAA T boxes; however, the 5'-UTR of the gene contains the initiator elemen ts frequently found in TATA-less genes. Avian I kappa B-alpha contains seven putative Rel/NF-kappa B binding sites. A CAT reporter construct containing the 5' upstream region of I kappa B-alpha was expressed wh en transfected into cells which produce I kappa B-alpha. This construc t, however, was not expressed in cells in which I kappa B-alpha activi ty was not induced, indicating that the regulatory elements which prom ote I kappa B-alpha expression are contained within 1000 nt of the tra nscription start site. Southern analysis suggests that I kappa B-alpha is present as a single-copy gene per haploid genome and is expressed in avian hematopoietic tissues, as well as lymphoid cells transformed by avian reticuloendotheliosis virus (REV-T).