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Eukaryotic Cell, November 2006, p. 1831-1837, Vol. 5, No. 11
1535-9778/06/$08.00+0     doi:10.1128/EC.00110-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Nitrogen Availability and TOR Regulate the Snf1 Protein Kinase in Saccharomyces cerevisiae

Marianna Orlova,¹ Ellen Kanter,^2, David Krakovich,¹ and Sergei Kuchin^1*

Department of Biological Sciences, University of Wisconsin—Milwaukee, Milwaukee, Wisconsin 53211,¹ Department of Genetics and Development, Columbia University, New York, New York 10032²

Received 17 April 2006/ Accepted 1 September 2006

In the yeast Saccharomyces cerevisiae, the Snf1 protein kinase of the Snf1/AMP-activated protein kinase (AMPK) family regulates a wide range of responses to stress caused by glucose deprivation. The stress signal is relayed via upregulation of Snf1, which depends on phosphorylation of its activation loop Thr210 residue by upstream kinases. Although Snf1 is also required for coping with various stresses unrelated to glucose deprivation, some evidence suggests a role for low-level basal activity of unphosphorylated Snf1, rather than a specific signaling function. We previously found that Snf1 is required for diploid pseudohyphal differentiation, a developmental response to nitrogen limitation. Here, we present evidence that Snf1 is directly involved in nitrogen signaling. First, genetic analyses suggest that pseudohyphal differentiation depends on the stimulatory phosphorylation of Snf1 at Thr210. Second, immunochemical data indicate that nitrogen limitation improves Thr210 phosphorylation. Analyses of pseudohyphal differentiation in cells with catalytically inactive and hyperactive Snf1 support the role of Snf1 activity. Finally, we show that Snf1 is negatively regulated by the rapamycin-sensitive TOR kinase which plays essential roles in signaling nitrogen and amino acid availability. This and other evidence implicate Snf1 in the integration of signals regarding nitrogen and carbon stress. TOR and Snf1/AMPK are highly conserved in evolution, and their novel functional interaction in yeast suggests similar mechanisms in other eukaryotes.

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* Corresponding author. Mailing address: Department of Biological Sciences, University of Wisconsin—Milwaukee, 3209 N. Maryland Ave., Milwaukee, WI 53211. Phone: (414) 229-3135. Fax: (414) 229-3926. E-mail: skuchin{at}uwm.edu.

Published ahead of print on 15 September 2006.

Present address: Department of Neurology, Columbia University, New York, NY 10032.

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Eukaryotic Cell, November 2006, p. 1831-1837, Vol. 5, No. 11
1535-9778/06/$08.00+0     doi:10.1128/EC.00110-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

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