Abstract
The kinetics of glucose transport and the transcription of all 20 members of the HXT hexose transporter gene family were studied in relation to the steady state in situ carbon metabolism of Saccharomyces cerevisiae CEN.PK113-7D grown in chemostat cultures. Cells were cultivated at a dilution rate of 0.10 h-1 under various nutrient-limited conditions (anaerobically glucose- or nitrogen-limited or aerobically glucose-, galactose-, fructose-, ethanol-, or nitrogen-limited), or at dilution rates ranging between 0.05 and 0.38 h-1 in aerobic glucose-limited cultures. Transcription of HXT1-HXT7 was correlated with the extracellular glucose concentration in the cultures. Transcription of GAL2, encoding the galactose transporter, was only detected in galactose-limited cultures. SNF3 and RGT2, two members of the HXT family that encode glucose sensors, were transcribed at low levels. HXT8-HXT17 transcripts were detected at very low levels. A consistent relationship was observed between the expression of individual HXT genes and the glucose transport kinetics determined from zero-trans influx of 14C-glucose during 5 s. This relationship was in broad agreement with the transport kinetics of Hxt1-Hxt7 and Gal2 deduced in previous studies on single-HXT strains. At lower dilution rates the glucose transport capacity estimated from zero-trans influx experiments and the residual glucose concentration exceeded the measured in situ glucose consumption rate. At high dilution rates, however, the estimated glucose transport capacity was too low to account for the in situ glucose consumption rate.
Highlights
The kinetics of glucose transport and the transcription of all 20 members of the HXT hexose transporter gene family were studied in relation to the steady state in situ carbon metabolism of Saccharomyces cerevisiae CEN.PK113-7D grown in chemostat cultures
The glucose transport kinetics of some individual HXT gene products have been analyzed in genetically modified yeast strains; it was found that a strain with null mutations in HXT1–HXT7 was not able to grow on various concentrations of glucose [5]
Physiology of S. cerevisiae CEN.PK113-7D in Steady State Chemostat Cultures—In aerobic glucose-limited chemostat cultures of S. cerevisiae CEN.PK113-7D grown at various dilution rates, the glucose consumption and product formation profiles were essentially as described previously [32]
Summary
The kinetics of glucose transport and the transcription of all 20 members of the HXT hexose transporter gene family were studied in relation to the steady state in situ carbon metabolism of Saccharomyces cerevisiae CEN.PK113-7D grown in chemostat cultures. The 20 members of this family include HXT1–HXT17, GAL2 (encoding the galactose transporter), and SNF3 and RGT2 (encoding putative sensors of high and low glucose concentrations, respectively) [4]. The glucose transport kinetics of some individual HXT gene products have been analyzed in genetically modified yeast strains; it was found that a strain with null mutations in HXT1–HXT7 (the hxt null strain) was not able to grow on various concentrations of glucose [5] When these seven HXT genes were expressed individually as single chromosomal copies in the hxt null strain, they were all able to confer growth on glucose or fructose medium with the exception of HXT5. The growth properties of the single-HXT strains differed on media with different glucose concentrations, suggesting that the genes are regulated differently in response to glucose or that they encode transporters with different affinities for glucose [5]
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