NEGATIVE TRANSCRIPTIONAL REGULATION OF THE CHICKEN NA+ K+-ATPASE ALPHA-1-SUBUNIT GENE/

Although the Na+/K+-ATPase alpha 1-subunit gene is ubiquitously expres sed in vertebrates, its level of expression varies among tissue and ce ll types. In spite of similar mRNA distribution in tissues of mammals and birds, the 5'-flanking regions of alpha 1-subunit genes exhibit re markable diversity; i.e., the core promoter activity of the TATA-less chicken alpha 1 gene strongly depends upon multiple Spl-based reoulati on (six Spl sites), whereas the promoter activity of the TATA-like rat alpha 1-subunit gene relies on the two Spl and additional positive re gulatory factors. Further analysis of the regulatory regions of the Na +/K+-ATPase alpha 1-subunit genes revealed that the vertebrate alpha 1 -subunit genes may share common inhibitory mechanisms for subtle trans criptional regulation; the core promoter activities can be either enha nced or repressed depending on the availability of inhibitory factors. Two potential candidates for such inhibitory elements in both avian a nd mammalian Na+/K+-ATPase alpha 1-subunit genes are (1) a newly ident ified element, GCCCTC, and (2) a GCF-binding sequence, NN[G/c]CG[G/cIG /cIG/c]CN, or its reverse complement. Gel retardation assays using the inhibitory region of the chicken gene and crude nuclear extracts from tissue-cultured chicken and mouse cells showed the existence of a set of proteins that bind to this region. The amounts of individual regul atory proteins in different cell types seem to vary, resulting in diff erential formation of DNA/protein complexes in different cell types. T hus, the regulation of Na+/K+-ATPase alpha 1-subunit gene expression u nder different cellular environment as well as in different cell types can be achieved by a shared mechanism; modulation of the ratio of the abundance of individual inhibitory factors.