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Molecular and Cellular Biology, July 1999, p. 4561-4571, Vol. 19, No. 7
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Std1 and Mth1 Proteins Interact with the Glucose Sensors To Control Glucose-Regulated Gene Expression in Saccharomyces cerevisiae

Martin C. Schmidt,1,* Rhonda R. McCartney,1 Xudong Zhang,1 Tommy S. Tillman,1 Harry Solimeo,1 Stefan Wölfl,2 Ciprian Almonte,3 and Simon C. Watkins3

Department of Molecular Genetics and Biochemistry1 and Department of Cell Biology and Physiology and Center for Biologic Imaging,3 University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, and Department of Cell and Molecular Biology, Hans-Knöll-Institut für Naturstoff-Forschung, Jena, Germany2

Received 17 February 1999/Returned for modification 25 March 1999/Accepted 6 April 1999

The Std1 protein modulates the expression of glucose-regulated genes, but its exact molecular role in this process is unclear. A two-hybrid screen for Std1-interacting proteins identified the hydrophilic C-terminal domains of the glucose sensors, Snf3 and Rgt2. The homologue of Std1, Mth1, behaves differently from Std1 in this assay by interacting with Snf3 but not Rgt2. Genetic interactions between STD1, MTH1, SNF3, and RGT2 suggest that the glucose signaling is mediated, at least in part, through interactions of the products of these four genes. Mutations in MTH1 can suppress the raffinose growth defect of a snf3 mutant as well as the glucose fermentation defect present in cells lacking both glucose sensors (snf3 rgt2). Genetic suppression by mutations in MTH1 is likely to be due to the increased and unregulated expression of hexose transporter genes. In media lacking glucose or with low levels of glucose, the hexose transporter genes are subject to repression by a mechanism that requires the Std1 and Mth1 proteins. An additional mechanism for glucose sensing must exist since a strain lacking all four genes (snf3 rgt2 std1 mth1) is still able to regulate SUC2 gene expression in response to changes in glucose concentration. Finally, studies with green fluorescent protein fusions indicate that Std1 is localized to the cell periphery and the cell nucleus, supporting the idea that it may transduce signals from the plasma membrane to the nucleus.

* Corresponding author. Mailing address: Department of Molecular Genetics and Biochemistry, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261. Phone: (412) 648-9243. Fax: (412) 624-1401. E-mail: mcs2{at}pop.pitt.edu.

Molecular and Cellular Biology, July 1999, p. 4561-4571, Vol. 19, No. 7
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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