Characterization of gene organization and generation of heterogeneous mRNA species of rat ISK protein.

The ISK protein is a novel, probably epithelial potassium channel which differs from conventional potassium channels in its structure, electrophysiology, and tissue distribution. In this investigation, we isolated and analyzed genomic and cDNA clones coding for the rat ISK protein to characterize the structural organization and expression pattern of the ISK protein gene. This analysis, together with primer extension and RNase protection experiments, indicated that the ISK protein mRNA is initiated from two different upstream exons and then encoded by an uninterrupted downstream exon covering the protein-coding and the 3'-untranslated regions of the mRNA. RNA blot hybridization analysis showed additional generation of several large species of mRNAs which result from inclusion of a part of the intron sequence and the 3'-flanking region of the ISK protein gene. Thus, the single ISK protein gene is involved in the production of multiple species of mRNAs through a variety of cellular mechanisms including transcription initiation at different sites, alternative RNA splicing, and polyadenylation at different sites. The heterogeneity of the ISK protein mRNAs may be associated with the emergence of the functional and regulatory diversity observed for potassium ion permeation in epithelial cells.