Potassium channels play important roles in shaping the electrical properties of excitable cells. Toward understanding the transcriptional regulation of a member of the inwardly rectifying potassium channel family, we have characterized the genomic structure and 5'-proximal promoter of the murine Kcnj2 gene (also referred to as IRK1 and Kir2.1). The Kcnj2 transcription unit is composed of two exons separated by a 5.5-kilobase pair intron. Deletion analysis of 5'-flanking sequences identified a promiscuously active 172-base pair minimal promoter, whereas expression from a construct containing additional upstream sequences was cell type-restricted. The minimal promoter contained an E box, a Y box, and three GC box consensus elements but lacked both TATA and CCAAT box elements. The activity of the minimal promoter was found to be controlled by a combination of the activities of the transcription factors Sp1, Sp3, and NF-Y. The interplay between Sp1, Sp3, and NF-Y within the architecture of the Kcnj2 promoter, the ubiquitous nature of these trans-acting factors, and the action of tissue-selective repressor element(s) may combine to enable a wide variety of cell types to differentially regulate Kcnj2 expression through transcriptional control.