Isolation and characterization of the LGT1 gene encoding a low-affinity glucose transporter from Torulaspora delbrueckii.
Torulaspora delbrueckii PYCC 5321 displayed a mediated glucose transport activity best fitted assuming a biphasic Michaelis-Menten kinetics with a low- and a high-affinity component. A genomic library of this yeast strain was used to transform a mutant of Saccharomyces cerevisiae deficient in glucose transport. Sequence analysis of a DNA fragment cloned, revealed the presence of a 1704 bp length ORF. This ORF, named LGT1, displayed a high homology to yeast glucose transporter genes. Functional characterization of the LGT1 gene product in S. cerevisiae revealed that it encodes a low-affinity transporter, able to mediate the uptake of glucose and fructose. In consonance with this, expression of LGT1 in S. cerevisiae was high in media containing 4% of glucose and almost undetectable in galactose as sole carbon source. In the absence of glucose, repression of LGT1 expression required the transcription factor Rgt1p. However, a functional Rgt1p does not appear to be required for a full induction of LGT1 at high glucose levels. Deletion of the gene coding for the general repressor Mig1p had no effect on LGT1 expression, but additional disruption of MIG2 in a mig1 background indicated that Mig2p or both Mig1p and Mig2p in a redundant way, act as repressors of LGT1 expression at high glucose concentrations. The GeneBank Accession No. for LGT1 is AY598344.
Alves-Araújo
Cecília
C
Department of Biology, University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal.
Hernandez-Lopez
Maria Jose
MJ
Prieto
Jose Antonio
JA
Randez-Gil
Francisca
F
Sousa
Maria João
MJ
D001483:Base Sequence; D001692:Biological Transport; D004271:DNA, Fungal / Q000737:chemistry / Q000235:genetics; D004268:DNA-Binding Proteins; D015966:Gene Expression Regulation, Fungal / Q000502:physiology; D005800:Genes, Fungal; D005947:Glucose / Q000378:metabolism*; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins / Q000235:genetics* / Q000378:metabolism; D016254:Mutagenesis, Insertional; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D012097:Repressor Proteins / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics; D004718:Saccharomycetales / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment; D015534:Trans-Activators / Q000235:genetics; D014157:Transcription Factors
D004271:DNA, Fungal; D004268:DNA-Binding Proteins; D009004:Monosaccharide Transport Proteins; C102114:RGT1 protein, S cerevisiae; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D005947:Glucose