Splicing of a retained intron within ROMK K1 channel RNA generates a novel set of isoforms in rat kidney

Beesley, A. H., B. Ortega, and S. J. White. Splicing of a retained intron within ROMK K1 channel RNA generates a novel set of isoforms in rat kidney. Am. J. Physiol. 276 (Cell Physiol. 45): C585–C592, 1999.—The renal outer medulla K1 channel (ROMK) family of K1 channels may constitute a major pathway for K1 secretion in the distal nephron. To date, four main isoforms of this gene have been identified in the rat that differ only in their NH2-terminal amino acids and that share a common ‘‘core exon’’ that determines the remaining protein sequence. Using RT-PCR, we have identified a new set of ROMK isoforms in rat kidney that are generated by the deletion of a region within the ROMK core sequence that is identifiable as a typical mammalian intron. This splicing event was shown to be reproducible in vitro by detection of deleted ROMK mRNAin Madin-Darby canine kidney (MDCK) cells stably transfected with the gene for ROMK2. Translation of the deletion variant of ROMK2 was confirmed in vitro and visualized in MDCK cells following transient transfection with an enhanced green fluorescent protein tag. The deletion in this core region is predicted to generate hydrophilic proteins that are approximately one-third of the size of native ROMK and lack membrane-spanning domains.