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Mol. Cell. Biol., 11 1996, 6419-6426, Vol 16, No. 11
S Ozcan, T Leong and M Johnston
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
function 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 glucose: (i)
in the absence of glucose, it functions as a transcriptional repressor;
(ii) high concentrations of glucose cause it to function as a
transcriptional activator; and (iii) in cells growing on low levels of
glucose, Rgt1p has a neutral role, neither repressing nor activating
transcription. Glucose alters Rgt1p function through a pathway that
includes two glucose sensors, Snf3p and Rgt2p, and Grr1p. The glucose
transporter Snf3p, which appears to be a low-glucose sensor, is required
for inhibition of Rgt1p repressor function by low levels of glucose. Rgt2p,
a glucose transporter that functions as a high-glucose sensor, is required
for conversion of Rgt1p into an activator by high levels of glucose. Grr1p,
a component of the glucose signaling pathway, is required both for
inactivation of Rgt1p repressor function by low levels of glucose and for
conversion of Rgt1p into an activator at high levels of glucose. Thus,
signals generated by two different glucose sensors act through Grr1p to
determine Rgt1p function.
Copyright © 1996, American Society for Microbiology
Rgt1p of Saccharomyces cerevisiae, a key regulator of glucose-induced genes, is both an activator and a repressor of transcription
Department of Genetics, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
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