S. Ozcan et al., RGT1P OF SACCHAROMYCES-CEREVISIAE, A KEY REGULATOR OF GLUCOSE-INDUCEDGENES, IS BOTH AN ACTIVATOR AND A REPRESSOR OF TRANSCRIPTION, Molecular and cellular biology, 16(11), 1996, pp. 6419-6426
The RGT1 gene of Saccharomyces cerevisiae plays a central role in the
glucose-induced expression of hexose transporter (HXT) genes, Genetic
evidence suggests that it encodes a repressor of the HXT genes whose f
unction is inhibited by glucose, Here, we report the isolation of RGT1
and demonstrate that it encodes a bifunctional transcription factor,
Rgt1p displays three different transcriptional modes in response to gl
ucose: (i) in the absence of glucose, it functions as a transcriptiona
l repressor; (ii) high concentrations of glucose cause it to function
as a transcriptional activator; and (iii) in cells growing on low leve
ls of glucose, Rgt1p has a neutral role, neither repressing nor activa
ting transcription, Glucose alters Rgt1p function through a pathway th
at includes two glucose sensors, Snf3p and Rgt2p, and Grr1p, The gluco
se transporter Snf3p, which appears to be a low-glucose sensor, is req
uired for inhibition of Rgt1p repressor function by low levels of gluc
ose, Rgt2p, a glucose transporter that functions as a high-glucose sen
sor, is required for conversion of Rgt1p into an activator by high lev
els of glucose, Grr1p, a component of the glucose signaling pathway, i
s required both for inactivation of Rgt1p repressor function by low le
vels of glucose and for conversion of Rgt1p into an activator at high
levels of glucose, Thus, signals generated by two different glucose se
nsors act through Grr1p to determine Rgt1p function.