PROMOTER CHARACTERIZATION OF THE HUMAN NA+ I- SYMPORTER/

The Na+/I- symporter (NIS) is the plasma membrane protein that mediate s active iodide uptake into thyroid follicular cells. To understand th e molecular mechanisms of human NIS (hNIS) gene regulation, the 2-kb i mmediate 5'-flanking region of hNIS was characterized. The tentative h NIS transcriptional start site was mapped to -375 nucleotide relative to the ATG site. Various 5'-genomic DNA fragments were tested for prom oter activity in thyroid and nonthyroid cells. Our results indicate th at the DNA regulatory elements in the 2-kb immediate 5'-flanking regio n were not sufficient to confer thyroid-selective transcription of the hNIS gene. In addition, hNIS minimal promoter was localized to a regi on of 144 bp that contains a 90-bp stretch of a highly conserved DNA f ragment between hNIS and rat NIS.