Schizosaccharomyces pombe UDP‐galactose transporter: identification of its functional form through cDNA cloning and expression in mammalian cells

The Schizosaccharomyces pombe UDP-galactose transporter cDNA (SpUGT cDNA), encoding the product of the gms1+ gene which consists of two exon sequences separated by a 173-bp intron, was cloned by RT-PCR. Its product, a hydrophobic protein of 353 amino acid residues resembling its human counterpart, was expressed in the Golgi membranes of UDP-galactose transporter-deficient Lec8 cells, and complemented the genetic defect of the mutant cells. This indicated that SpUGT cDNA encodes the functional S. pombe UDP-galactose transporter. The product of an ORF found in the second exon, which was previously assumed to be the S. pombe UDP-galactose transporter, thus represents an inactive, truncated form of the SpUGT protein.