Genomic organization and promoter analysis of the human G-protein-coupled K+ channel Kir3.1 (KCNJ3/HGIRK1).

The class of G-protein-coupled inwardly rectifying K+ channels is composed of at least four members, Kir3.1, Kir3.2, Kir3.3, and Kir3.4. Here we describe the genomic organization of human Kir3.1 (locus designated KCNJ3; cDNA previously named HGIRK1) and the characterization of its major promoter used in hippocampus. The Kir3.1 gene contains three exons separated by two introns, and its total length exceeds 45 kb. The two transmembrane domains, pore region, and part of the putative carboxyl terminus are encoded by exon 1, whereas the remainder of the tail is encoded by exons 2 and 3. The mRNA transcription initiation site was established, and the first 1520 bp upstream were sequenced; this region lacked a traditional TATA or CAAT box, but contained a GC-rich region as well as various putative transcription factor-binding elements. The 1520 bp upstream and 84 bp downstream of the transcription initiation site were tested for promoter activity in GH4-C1 cells. This sequence of 1604 bp contains a number of fragments that either stimulate or repress transcription, as tested by transient expression of various Kir3.1 promoter/luciferase fusion gene constructs in GH4-C1 cells. To our knowledge, this is the first promoter that has been isolated and characterized for an inwardly rectifying potassium channel. Additional data suggest the existence of another promoter that can drive transcription of Kir3.1 mRNA from a distinct initiation site.