Isolation and characterization of two distinct myo-inositol transporter genes of Saccharomyces cerevisiae.
By the complementation of a yeast mutant defective in myo-inositol transport (Nikawa, J., Nagumo, T., and Yamashita, S. (1982) J. Bacteriol. 150, 441-446), we isolated two myo-inositol transporter genes, ITR1 and ITR2, from a yeast gene library. The ITR1 and ITR2 genes contained long open reading frames capable of encoding 584 and 612 amino acids with calculated relative molecular masses of 63,605 and 67,041, respectively. The sequence similarity between the ITR1 and ITR2 products was extremely high, suggesting that the two genes arose from a common ancestor. Both gene products show significant sequence homology with a superfamily of sugar transporters, including human HepG2 hepatoma/erythrocyte glucose transporter and Escherichia coli xylose transporter. Hydropathy analysis indicated that the ITR1 and ITR2 products are both hydrophobic and contain 12 putative membrane-spanning regions. Thus, yeast myo-inositol transporters could be classified into the sugar transporter superfamily. Gene disruption and tetrad analysis showed that yeast cells contain two separate myoinositol transporters. The ITR1 product was the major transporter and the ITR2 product the minor one in cells grown in minimum medium containing glucose. Northern blot analysis showed that ITR1 mRNA was much more abundant than ITR2 mRNA. The previously isolated myo-inositol transport mutant was determined to be defective in ITR1.
Nikawa
J
J
Department of Biochemistry, Gunma University School of Medicine, Maebashi, Japan.
Tsukagoshi
Y
Y
Yamashita
S
S
D000595:Amino Acid Sequence; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D003001:Cloning, Molecular; D004271:DNA, Fungal / Q000235:genetics / Q000302:isolation & purification; D005656:Fungal Proteins / Q000235:genetics* / Q000378:metabolism; D005800:Genes, Fungal; D005816:Genetic Complementation Test; D005838:Genotype; D006801:Humans; D007294:Inositol / Q000378:metabolism*; D007700:Kinetics; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins / Q000235:genetics; D005810:Multigene Family; D011487:Protein Conformation; D012333:RNA, Messenger / Q000235:genetics; D015183:Restriction Mapping; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D012689:Sequence Homology, Nucleic Acid; D014158:Transcription, Genetic
D002352:Carrier Proteins; D004271:DNA, Fungal; D005656:Fungal Proteins; C069143:ITR1 protein, S cerevisiae; C069144:ITR2 protein, S cerevisiae; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D012333:RNA, Messenger; D029701:Saccharomyces cerevisiae Proteins; D007294:Inositol