Genetic analysis of glucose regulation in Saccharomyces cerevisiae: control of transcription versus mRNA turnover

A major determinant of the steady-state level of the mRNA encoding the iron protein (Ip) subunit of succinate dehydrogenase of yeast is its rate of turnover. This mRNA is significantly more stable in glycerol than in glucose media. Many other genes, for example SUC2, that are repressed in the presence of glucose are believed to be controlled at the level of transcription. The present study elucidates differences in the regulatory mechanisms by which glucose controls the transcription and turnover of the SUC2 and Ip mRNAs. The signaling pathway for glucose repression at the transcriptional level has been associated with a number of gene products linking glucose uptake with nuclear events. We have investigated whether the same genes are involved in the control of Ip mRNA stability. Phosphorylation of glucose or fructose is critical in triggering the transcript's degradation, but any hexokinase will do. Of the other known genes examined, most, with the exception of REG1, are not involved in determining the differential stability of the Ip transcript. Finally, our results indicate that differential stability on different carbon sources also plays a role in determining the steady-state level of the SUC2 mRNA. Thus, glucose repression includes both transcriptional and post-transcriptional mechanisms.