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Eukaryotic Cell, January 2006, p. 174-179, Vol. 5, No. 1
1535-9778/06/$08.00+0     doi:10.1128/EC.5.1.174-179.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Deletion of RTS1, Encoding a Regulatory Subunit of Protein Phosphatase 2A, Results in Constitutive Amino Acid Signaling via Increased Stp1p Processing

Nadine Eckert-Boulet,1,2 Katrin Larsson,1,{ddagger} Boqian Wu,1 Peter Poulsen,1 Birgitte Regenberg,2,{dagger} Jens Nielsen,2 and Morten C. Kielland-Brandt1*

Carlsberg Laboratory, Gamle Carlsberg Vej 10, DK-2500 Copenhagen Valby, Denmark,1 Center for Microbial Biotechnology, BioCentrum-DTU, Technical University of Denmark, DK-2800 Kgs Lyngby, Denmark2

Received 21 September 2005/ Accepted 4 November 2005

In Saccharomyces cerevisiae, extracellular amino acids are sensed at the plasma membrane by the SPS sensor, consisting of the transporter homologue Ssy1p, Ptr3p, and the endoprotease Ssy5p. Amino acid sensing results in proteolytic truncation of the transcription factors Stp1p and Stp2p, followed by their relocation from the cytoplasm to the nucleus, where they activate transcription of amino acid permease genes. We screened a transposon mutant library for constitutively signaling mutants, with the aim of identifying down-regulating components of the SPS-mediated pathway. Three isolated mutants were carrying a transposon in the RTS1 gene, which encodes a regulatory subunit of protein phosphatase 2A. We investigated the basal activity of the AGP1 and BAP2 promoters in rts1{Delta} cells and found increased transcription from these promoters, as well as increased Stp1p processing, even in the absence of amino acids. Based on our findings we propose that the phosphatase complex containing Rts1p keeps the SPS-mediated pathway down-regulated in the absence of extracellular amino acids by dephosphorylating a component of the pathway.

* 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.

{ddagger} Present address: Bioinvent Int. AB, Sölvegatan 41, SE-22370 Lund, Sweden.

{dagger} Present address: Institut für Mikrobiologie, Goethe-Universität Frankfurt, Marie Curie Strasse 9, D-60439, Frankfurt-am-Main, Germany.

Eukaryotic Cell, January 2006, p. 174-179, Vol. 5, No. 1
1535-9778/06/$08.00+0     doi:10.1128/EC.5.1.174-179.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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