Rgt1, a glucose sensing transcription factor, is required for transcriptional repression of the HXK2 gene in Saccharomyces cerevisiae.

Expression of HXK2, a gene encoding a Saccharomyces cerevisiae bifunctional protein with catalytic and regulatory functions, is controlled by glucose availability, being activated in the presence of glucose and inhibited when the levels of the sugar are low. In the present study, we identified Rgt1 as a transcription factor that, together with the Med8 protein, is essential for repression of the HXK2 gene in the absence of glucose. Rgt1 represses HXK2 expression by binding specifically to the motif (CGGAAAA) located at -395 bp relative to the ATG translation start codon in the HXK2 promoter. Disruption of the RGT1 gene causes an 18-fold increase in the level of HXK2 transcript in the absence of glucose. Rgt1 binds to the RGT1 element of HXK2 promoter in a glucose-dependent manner, and the repression of target gene depends on binding of Rgt1 to DNA. The physiological significance of the connection between two glucose-signalling pathways, the Snf3/Rgt2 that causes glucose induction and the Mig1/Hxk2 that causes glucose repression, was also analysed.