THE CANINE SODIUM MYO-INOSITOL COTRANSPORTER GENE - STRUCTURAL ORGANIZATION AND CHARACTERIZATION OF THE PROMOTER/

The sodium/myo-inositol cotransporter (SMIT) is a plasma membrane prot ein catalyzing transfer of myoinositol into cells against a considerab le concentration gradient using the electrochemical potential of sodiu m across the cell membrane, Transcription of the SMIT gene is markedly stimulated when cells are exposed to a hypertonic environment resulti ng in increased abundance of SMIT mRNA and increased SMIT activity, Th e increased accumulation of myo-inositol protects cells from the delet erious effects of hypertonicity, In an effort toward understanding tra nscriptional regulation, we cloned canine genomic DNA fragments contai ning the SMIT gene. The gene is 37 kb in size consisting of 2 exons an d a large intron of 25 kb, The entire open reading frame is in the sec ond exon, The promoter of the gene is highly active due to a GC-rich s equence. Ribonuclease protection assay using a riboprobe complementary to the 5' end of the gene confirmed that the promoter of the gene is stimulated by hypertonicity, The promoters and regulatory sequences of the SMIT gene and the betaine transporter gene, another gene regulate d by hypertonicity, appear to be different. (C) 1997 Academic Press.