Glucose repression of the yeast ADH2 gene occurs through multiple mechanisms, including control of the protein synthesis of its transcriptional activator, ADR1.

Abstract

The rate of ADH2 transcription increases dramatically when Saccharomyces cerevisiae cells are shifted from glucose to ethanol growth conditions. Since ADH2 expression under glucose growth conditions is strictly dependent on the dosage of the transcriptional activator ADR1, we investigated the possibility that regulation of the rate of ADR1 protein synthesis plays a role in controlling ADR1 activation of ADH2 transcription. We found that the rate of ADR1 protein synthesis increased 10- to 16-fold within 40 to 60 min after glucose depletion, coterminous with initiation of ADH2 transcription. Changes in ADR1 mRNA levels contributed only a twofold effect on ADR1 protein synthetic differences. The 510-nt untranslated ADR1 mRNA leader sequence was found to have no involvement in regulating the rate of ADR1 protein synthesis. In contrast, sequences internal to ADR1 coding region were determined to be necessary for controlling ADR1 translation. The ADR1c mutations which enhance ADR1 activity under glucose growth conditions did not affect ADR1 protein translation. ADR1 was also shown to be multiply phosphorylated in vivo under both ethanol and glucose growth conditions. Our results indicate that derepression of ADH2 occurs through multiple mechanisms involving the ADR1 regulatory protein.