Cloning, gene structure and genomic localization of an orphan transporter from mouse kidney with six alternatively-spliced isoforms

Two genes were identified and characterized that express cDNAs related to p reviously identified neurotransmitter and/or osmolyte transporters, but, wh ich are expressed specifically in the kidney. RNA transcribed from one of t hese two genes (XT2) was found to undergo an extensive degree of alternativ e splicing to generate six distinct isoforms. The intron-exon structure of the XT2 gene and the sites of alternative splicing were identified. Express ion of the second gene (XT3) was found to be conserved in human kidney, and partial sequence was obtained from a human cDNA library. The expressions o f both XT2 and XT3 RNAs were determined in mouse and human tissues, respect ively, and the locations of the two genes within the mouse genome were iden tified. Screening experiments to identify the substrate(s) of these protein s failed to identify specific uptake with any of the tested compounds; howe ver, immunofluorescent microscopy demonstrated that epitope-tagged variants of the protein products of the XT2 and XT3 cDNAs were present on the plasm a membrane of transfected cells.