A nitrogen-limited, glucose-repressed, continuous culture of Saccharomyces cerevisiae.
Glucose-repressed growth of Saccharomyces cerevisiae was analysed in a nitrogen-limited continuous culture at different dilution rates (D). The glucose consumption of the yeast decreased from 3.4 g g-1 h-1 to 3.0 g g-1 h-1 when D was decreased from 0.3 h-1 to 0.15 h-1. No transcripts of the SUC2 and HXK1 genes, encoding, respectively, invertase and hexokinase isoenzyme 1, could be detected. Because both genes are regulated by glucose repression at the transcriptional level, this confirmed that the culture was glucose repressed at every D. During the decrease in D, no change in the activities or mRNA levels of key enzymes in carbon metabolism was observed, except for alcohol dehydrogenases I and II and phosphoglucomutase. These enzymes increased in activity and/or mRNA level when D was decreased, which was also observed in glucose- and galactose-limited continuous cultures. This demonstrates that the expression levels of alcohol dehydrogenases I and II, and also phosphoglucomutase, are coupled to the growth rate of the organism. A comparison between the alcohol dehydrogenase II activity in glucose- and nitrogen-limited continuous cultures demonstrated that the growth rate contributes as much to repression of alcohol dehydrogenase II activity as does glucose. Both the glucose consumption and the activity of the glycolytic enzymes were relatively constant when D was decreased and, as a consequence, the concentrations of intracellular metabolites remained constant. A slight decrease in the glucose 6-phosphate concentration was observed, which could be caused by the slight decrease in glucose consumption at low D values.(ABSTRACT TRUNCATED AT 250 WORDS)
Department of Molecular Cell Biology, University of Utrecht, The Netherlands.
L N
LN
Sierkstra
E G
EG
ter Schure
J M
JM
Verbakel
C T
CT
Verrips
D002244:Carbon / Q000378:metabolism; D004798:Enzymes / Q000235:genetics / Q000378:metabolism; D005798:Genes, Bacterial; D005947:Glucose / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism; D010101:Oxygen Consumption; D012331:RNA, Fungal / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*
D004798:Enzymes; D012331:RNA, Fungal; D012333:RNA, Messenger; D002244:Carbon; D005947:Glucose; D009584:Nitrogen