The expression in Saccharomyces cerevisiae of a glucose/xylose symporter from Candida intermedia is affected by the presence of a glucose/xylose facilitator.
Two glucose/xylose transporter genes from Candida intermedia were recently cloned and characterized: GXF1, which encodes a glucose/xylose facilitator; and GXS1, which encodes a glucose/xylose proton symporter. Here we report the functional expression of these transporters in Saccharomyces cerevisiae. While Gxf1p seems to be fully functional in S. cerevisiae, the symporter Gxs1p exhibits very low glucose/xylose transport activity, which could not be ascribed to insufficient production of the protein or incorrect subcellular localization. In addition, co-expression of glucose/xylose facilitators with Gxs1p strongly reduced GXS1 mRNA levels, and consequently symport activity, in glucose-grown, but not in ethanol-grown, cells. The observed decrease in GXS1 transcript levels seems to be related to an enhanced glucose influx mediated by glucose facilitator protein(s), and not to a specific interaction between Gxs1p and other transporters. We found GXS1 mRNA levels to be severely reduced as a result of glucose addition, and we show that this effect takes place at the level of GXS1 mRNA stability. Our results suggest that a decrease in mRNAs encoding high-affinity/active sugar transport systems may be a widespread and conserved mechanism in yeasts, limiting expression of these proteins whenever their activity is dispensable.
Centro de Recursos Microbiológicos (CREM), Department of Life Sciences, Faculty of Sciences and Technology, New University of Lisbon, 2829-516 Caparica, Portugal.
Maria José
MJ
Leandro
Centro de Recursos Microbiológicos (CREM), Department of Life Sciences, Faculty of Sciences and Technology, New University of Lisbon, 2829-516 Caparica, Portugal.
Isabel
I
Spencer-Martins
Centro de Recursos Microbiológicos (CREM), Department of Life Sciences, Faculty of Sciences and Technology, New University of Lisbon, 2829-516 Caparica, Portugal.
Paula
P
Gonçalves
D002175:Candida / Q000145:classification / Q000235:genetics* / Q000378:metabolism*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism*; D020871:RNA Stability / Q000187:drug effects; D012331:RNA, Fungal / Q000187:drug effects; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D027981:Symporters / Q000235:genetics / Q000378:metabolism*; D014994:Xylose / Q000378:metabolism
D005656:Fungal Proteins; D009004:Monosaccharide Transport Proteins; D012331:RNA, Fungal; D027981:Symporters; D014994:Xylose; D005947:Glucose