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Eukaryotic Cell, June 2005, p. 1116-1124, Vol. 4, No. 6
1535-9778/05/$08.00+0     doi:10.1128/EC.4.6.1116-1124.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Constitutive Signal Transduction by Mutant Ssy5p and Ptr3p Components of the SPS Amino Acid Sensor System in Saccharomyces cerevisiae

Peter Poulsen,1 Boqian Wu,1 Richard F. Gaber,2 and Morten C. Kielland-Brandt1*

Carlsberg Laboratory, DK-2500 Copenhagen Valby, Denmark,1 Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, Evanston, Illinois 60208-35002

Received 2 March 2005/ Accepted 7 April 2005

Amino acids in the environment of Saccharomyces cerevisiae can transcriptionally activate a third of the amino acid permease genes through a signal that originates from the interaction between the extracellular amino acids and an integral plasma membrane protein, Ssy1p. Two plasma membrane-associated proteins, Ptr3p and Ssy5p, participate in the sensing, which results in cleavage of the transcription factors Stp1p and Stp2p, removing 10 kDa of the N terminus of each of them. This confers the transcription factors with the ability to gain access to the nucleus and activate transcription of amino acid permease genes. To extend our understanding of the role of Ptr3p and Ssy5p in this amino acid sensing process, we have isolated constitutive gain-of-function mutants in these two components by using a genetic screening in which potassium uptake is made dependent on amino acid signaling. Mutants which exhibit inducer-independent processing of Stp1p and activation of the amino acid permease gene AGP1 were obtained. For each component of the SPS complex, constitutive signaling by a mutant allele depended on the presence of wild-type alleles of the other two components. Despite the signaling in the absence of inducer, the processing of Stp1p was more complete in the presence of inducer. Dose response assays showed that the median effective concentration for Stp1p processing in the mutant cells was decreased; i.e., a lower inducer concentration is needed for signaling in the mutant cells. These results suggest that the three sensor components interact intimately in a complex rather than in separate reactions and support the notion that the three components function as a complex.

* Corresponding author. Mailing address: Carlsberg Laboratory, Gamle Carlsberg Vej 10, DK-2500 Copenhagen Valby, Denmark. Phone: (45) 3327 5331. Fax: (45) 3327 4765. E-mail: mkb{at}crc.dk.

Eukaryotic Cell, June 2005, p. 1116-1124, Vol. 4, No. 6
1535-9778/05/$08.00+0     doi:10.1128/EC.4.6.1116-1124.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Liu, Z., Thornton, J., Spirek, M., Butow, R. A. (2008). Activation of the SPS Amino Acid-Sensing Pathway in Saccharomyces cerevisiae Correlates with the Phosphorylation State of a Sensor Component, Ptr3. Mol. Cell. Biol. 28: 551-563 [Abstract] [Full Text]  
  • Wu, B., Ottow, K., Poulsen, P., Gaber, R. F., Albers, E., Kielland-Brandt, M. C. (2006). Competitive intra- and extracellular nutrient sensing by the transporter homologue Ssy1p. JCB 173: 327-331 [Abstract] [Full Text]  
  • Poulsen, P., Lo Leggio, L., Kielland-Brandt, M. C. (2006). Mapping of an Internal Protease Cleavage Site in the Ssy5p Component of the Amino Acid Sensor of Saccharomyces cerevisiae and Functional Characterization of the Resulting Pro- and Protease Domains by Gain-of-Function Genetics. Eukaryot Cell 5: 601-608 [Abstract] [Full Text]  
  • Eckert-Boulet, N., Larsson, K., Wu, B., Poulsen, P., Regenberg, B., Nielsen, J., Kielland-Brandt, M. C. (2006). Deletion of RTS1, Encoding a Regulatory Subunit of Protein Phosphatase 2A, Results in Constitutive Amino Acid Signaling via Increased Stp1p Processing. Eukaryot Cell 5: 174-179 [Abstract] [Full Text]  


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