Differential post-transcriptional regulation of yeast mRNAs in response to high and low glucose concentrations.

Glucose regulates yeast gene expression at both transcriptional and post-transcriptional levels. Glucose strongly represses the transcription of the gluconeogenic genes, FBP1 and PCK1, and accelerates the degradation of their mRNAs. Together these mechanisms are responsible for the rapid decrease in gluconeogenic enzyme synthesis when yeast cells switch to glycolytic metabolism. In this study, we show that accelerated gluconeogenic mRNA degradation can be triggered by low concentrations of glucose (<0. 02%). This sets the FBP1 and PCK1 mRNAs apart from other glucose-sensitive mRNAs, such as the Ip mRNA, which only responds to high glucose concentrations (>1%). We also show that accelerated gluconeogenic mRNA degradation is co-ordinated with transcriptional repression by common signalling components that include sugar kinases and Ras-cAMP signalling. Furthermore, the ability of the low glucose signal to trigger accelerated gluconeogenic mRNA degradation depends upon the low glucose sensor, Snf3p, but not on the high glucose sensor, Rgt2p. Also, this response is influenced by reg1 and ume5 mutations, but not by grr1 or rgt1 mutations. Our data suggest that several signalling pathways co-ordinate differential post-transcriptional and transcriptional responses in yeast, depending upon the amount of glucose available in the medium.