Structure and regulation of the gene encoding avian inhibitor of nuclear factor κB-α

The Rel/NF-κB family of transcription factors exist in the cytoplasm as inactive complexes in association with an inhibitory protein called IκB-α. We have isolated a clone containing the avian IκB-α gene from a chicken genomic library. Avian IκB- α is devoid of any recognizable promoter elements, i.e., TATA and CAAT boxes; however, the 5′-UTR of the gene contains the initiator elements frequently found in TATA-less genes. Avian IκB- α contains seven putative Rel/NF-κB binding sites. A CAT reporter construct containing the 5′ upstream region of IκB- α was expressed when transfected into cells which produce IKB-α. This construct, however, was not expressed in cells in which IκB-α activity was not induced, indicating that the regulatory elements which promote IκB- α expression are contained within 1000 nt of the transcription start site. Southern analysis suggests that IκB- α 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).