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To identify common regulatory sequences in the promoters of genes, transcription of 31 genes of Saccharomyces cerevisiaewas analysed during the transient response to a glucose pulse in a chemostat culture. mRNA levels were monitored during the subsequent excess glucose, ethanol and acetate phases, while other conditions were kept constant. This setup allowed a direct comparison between regulation by glucose, ethanol and acetate.

In Saccharomyces cerevisiae, the structural genes ACS1 and ACS2 each encode an isoenzyme of acetyl-CoA synthetase (ACS; EC 6.2.1.1). Involvement of glucose catabolite repression in regulation of the two isoenzymes was investigated by following ACS activity after glucose pulses (100 mM) to ethanol-limited chemostat cultures. In wild-type S. cerevisiae and in an isogenic strain in which ACS2 had been disrupted, ACS activity decreased after a glucose pulse. No such inactivation was observed in a strain in which ACS1 was disrupted. Western blots demonstrated that the ACS1 product, but not the ACS2 product, was degraded after a glucose pulse. Inactivation kinetics of the ACS1 product resembled those of isocitrate lyase.