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Journal of Bacteriology, February 2000, p. 647-654, Vol. 182, No. 3
Biology Department, Queens College and the
Graduate School of the City University of New York, Flushing, New
York 11367
Received 2 July 1999/Accepted 5 November 1999
Organisms such as Saccharomyces capable of utilizing
several different sugars selectively ferment glucose when less
desirable carbon sources are also available. This is achieved by
several mechanisms. Glucose down-regulates the transcription of
genes involved in utilization of these alternate carbon sources.
Additionally, it causes posttranslational modifications of enzymes and
transporters, leading to their inactivation and/or degradation.
Two glucose sensing and signaling pathways stimulate glucose-induced
inactivation of maltose permease. Pathway 1 uses Rgt2p as a sensor
of extracellular glucose and causes degradation of maltose permease
protein. Pathway 2 is dependent on glucose transport and stimulates
degradation of permease protein and very rapid inactivation of maltose
transport activity, more rapid than can be explained by loss of protein alone. In this report, we characterize signal generation through pathway 2 using the rapid inactivation of maltose transport activity as
an assay of signaling activity. We find that pathway 2 is dependent on
HXK2 and to a lesser extent HXK1. The
correlation between pathway 2 signaling and glucose repression suggests
that these pathways share common upstream components. We demonstrate
that glucose transport via galactose permease is able to stimulate
pathway 2. Moreover, rapid transport and fermentation of a number of
fermentable sugars (including galactose and maltose, not just glucose)
are sufficient to generate a pathway 2 signal. These results indicate that pathway 2 responds to a high rate of sugar fermentation and monitors an intracellular metabolic signal. Production of this signal
is not specific to glucose, glucose catabolism, glucose transport by
the Hxt transporters, or glucose phosphorylation by hexokinase 1 or 2. Similarities between this yeast glucose sensing pathway and glucose
sensing mechanisms in mammalian cells are discussed.
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Metabolic Signals Trigger Glucose-Induced
Inactivation of Maltose Permease in Saccharomyces


*
Corresponding author. Mailing address: Biology
Department, Queens College and the Graduate School of CUNY, 65-30 Kissena Blvd., Flushing, NY 11367. Phone: (718) 997-3410. Fax: (718)
997-3445. E-mail: corinne_michels{at}qc.edu.
Present address: Department of Bioinformatics, Regeneron
Pharmaceuticals, Inc., Tarrytown, NY 10591.
Present address: Department of Chemistry, University of
California
Berkeley, Berkeley, CA 94720.
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