title: The HXT1 gene product of Saccharomyces cerevisiae is a new member of the family of hexose transporters.
abstract: Two novel genes affecting hexose transport in the yeast Saccharomyces cerevisiae have been identified. The gene HXT1 (hexose transport), isolated from plasmid pSC7, was sequenced and found to encode a hydrophobic protein which is highly homologous to the large family of sugar transporter proteins from eucaryotes and procaryotes. Multicopy expression of the HXT1 gene restored high-affinity glucose transport to the snf3 mutant, which is deficient in a significant proportion of high-affinity glucose transport. HXT1 was unable to complement the snf3 growth defect in low copy number. The HXT1 protein was found to contain 12 putative membrane-spanning domains with a central hydrophilic domain and hydrophilic N- and C-terminal domains. The HXT1 protein is 69% identical to GAL2 and 66% identical to HXT2, and all three proteins were found to have a putative leucine zipper motif at a consensus location in membrane-spanning domain 2. Disruption of the HXT1 gene resulted in loss of a portion of high-affinity glucose and mannose transport, and wild-type levels of transport required both the HXT1 and SNF3 genes. Unexpectedly, expression of beta-galactosidase activity by using a fusion of the lacZ gene to the HXT1 promoter in a multicopy plasmid was maximal during lag and early exponential phases of growth, decreasing approximately 100-fold upon further entry into exponential growth. Deletion analysis of pSC7 revealed the presence of another gene (called ORF2) capable of suppressing the snf3 null mutant phenotype by restoring high-affinity glucose transport and increased low-affinity transport.
authors.affiliation: Department of Viticulture and Enology, University of California, Davis 95616.
authors.forename: D A
authors.initials: DA
authors.lastname: Lewis
authors.forename: L F
authors.initials: LF
authors.lastname: Bisson
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D004271:DNA, Fungal / Q000235:genetics / Q000302:isolation & purification; D004926:Escherichia coli / Q000235:genetics; D005800:Genes, Fungal; D005816:Genetic Complementation Test; D005838:Genotype; D005947:Glucose / Q000378:metabolism; D006601:Hexoses / Q000378:metabolism; D007700:Kinetics; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins / Q000235:genetics* / Q000378:metabolism; D010957:Plasmids; D015183:Restriction Mapping; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D012689:Sequence Homology, Nucleic Acid
chemical_list: D004271:DNA, Fungal; D006601:Hexoses; D009004:Monosaccharide Transport Proteins; D005947:Glucose