Glucose uptake kinetics and transcription of HXT genes in chemostat cultures of Saccharomyces cerevisiae.

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.