GLUCOSE SENSING AND SIGNALING BY 2 GLUCOSE RECEPTORS IN THE YEAST SACCHAROMYCES-CEREVISIAE

How eukaryotic cells sense availability of glucose, their preferred ca rbon and energy source, is an important, unsolved problem, Bakers' yea st (Saccharomyces cerevisiae) asses two glucose transporter homologs, Snf3 and Rgt2 as glucose sensors that generate a signal for induction of expression of genes encoding hexose transporters (HXT genes). We pr esent evidence that these proteins generate an intracellular glucose s ignal without transporting glucose. The Snf3 and Rgt2 glucose sensors contain unusually long C-terminal tails that are predicted to be in th e cytoplasm. These tails appear to be the signaling domains of Snf3 an d Rgt2 because they are necessary for glucose signaling by Snf3 and Rg t2, and transplantation of the C-terminal tail of Snf3 onto the Hxt1 a nd Hxt2 glucose transporters converts them into glucose sensors that c an generate a signal for glucose-induced HXT gene expression. These re sults support the idea that yeast senses glucose using two modified gl ucose transporters that serve as glucose receptors.