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Eukaryotic Cell, October 2004, p. 1147-1153, Vol. 3, No. 5
1535-9778/04/$08.00+0     DOI: 10.1128/EC.3.5.1147-1153.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Integration of Stress Responses: Modulation of Calcineurin Signaling in Saccharomyces cerevisiae by Protein Kinase A

Kimberly A. Kafadar and Martha S. Cyert^*

Department of Biological Sciences, Stanford University, Stanford, California

Received 16 June 2004/ Accepted 19 July 2004

Calcineurin is a Ca²⁺/calmodulin-dependent protein phosphatase required for Saccharomyces cerevisiae to adapt to a variety of environmental stresses. Once activated, calcineurin dephosphorylates the Zn-finger transcription factor Crz1p/Tcn1p, causing it to accumulate in the nucleus where it activates gene expression. Here we show that cyclic AMP-dependent protein kinase A (PKA) phosphorylates and negatively regulates Crz1p activity by inhibiting its nuclear import. Activation of PKA in vivo decreases Crz1p-dependent transcription. PKA phosphorylates Crz1p in vitro, and we identify specific residues required for this phosphorylation, all of which reside in or adjacent to the nuclear localization signal. Mutation of these residues to alanine results in increased nuclear import of Crz1p and results in higher levels of both basal and Ca²⁺-induced Crz1p transcriptional activity. PKA regulates the general stress response in yeast and coordinates this response with nutrient availability. In contrast, calcineurin regulates the cellular response to a restricted set of environmental insults. Thus, these studies identify a specific biochemical mechanism through which the activities of multiple stress-activated signaling pathways are integrated in vivo.

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* Corresponding author. Mailing address: Department of Biological Sciences, Stanford University, 337 Campus Dr., Lokey Building, Stanford, CA 94305-5020. Phone: (650) 723-9970. Fax: (650) 723-0155. E-mail: mcyert{at}stanford.edu.

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Eukaryotic Cell, October 2004, p. 1147-1153, Vol. 3, No. 5
1535-9778/04/$08.00+0     DOI: 10.1128/EC.3.5.1147-1153.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

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