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

The kinetics of glucose transport and the transcription of all 20 members o f the HXT hexose transporter gene family were studied in relation to the st eady 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 glucos e- or nitrogen-limited or aerobically glucose-, galactose-, fructose-, etha nol-, 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 w as correlated with the extracellular glucose concentration in the cultures. Transcription of GAL2, encoding the galactose transporter, was only detect ed in galactose-limited cultures. SNF3 and RGT2, two members of the HXT fam ily that encode glucose sensors, were transcribed at low levels. HXT8-HXT17 transcripts were detected at very low levels. A consistent relationship wa s observed between the expression of individual HXT genes and the glucose t ransport kinetics determined from zero-trans influx of C-14-glucose during 5 s, This relationship was in broad agreement with the transport kinetics o f Hxt1-Hxt7 and Gal2 deduced in previous studies on single-HXT strains. At lower dilution rates the glucose transport capacity estimated from zero-tra ns influx experiments and the residual glucose concentration exceeded the m easured 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.