TORC1 and TORC2 work together to regulate ribosomal protein S6 phosphorylation in Saccharomyces cerevisiae

  • Mol Biol Cell. 2016 Jan 15;27(2):397-409. doi: 10.1091/mbc.E15-08-0594.
Seda Yerlikaya  1 ,  Madeleine Meusburger  1 ,  Romika Kumari  2 ,  Alexandre Huber  1 ,  Dorothea Anrather  3 ,  Michael Costanzo  4 ,  Charles Boone  4 ,  Gustav Ammerer  3 ,  Pavel V Baranov  2 ,  Robbie Loewith  5
Affiliations
  • 1. Department of Molecular Biology and Institute of Genetics and Genomics of Geneva, University of Geneva, CH-1211 Geneva, Switzerland.
  • 2. School of Biochemistry and Cell Biology, University College Cork, Cork, Ireland.
  • 3. Max F. Perutz Laboratories, Department of Biochemistry, University of Vienna, A1030 Vienna, Austria.
  • 4. Banting and Best Department of Medical Research, Donnelly Center for Cellular and Biomolecular Research, University of Toronto, Toronto, ON M5S 3E1, Canada.
  • 5. Department of Molecular Biology and Institute of Genetics and Genomics of Geneva, University of Geneva, CH-1211 Geneva, Switzerland Swiss National Centre for Competence in Research Programme Chemical Biology, 1211 Geneva, Switzerland [email protected].
PMID: 26582391 DOI: 10.1091/mbc.E15-08-0594
Abstract

Nutrient-sensitive phosphorylation of the S6 protein of the 40S subunit of the eukaryote ribosome is highly conserved. However, despite four decades of research, the functional consequences of this modification remain unknown. Revisiting this enigma in Saccharomyces cerevisiae, we found that the regulation of Rps6 phosphorylation on Ser-232 and Ser-233 is mediated by both TOR complex 1 (TORC1) and TORC2. TORC1 regulates phosphorylation of both sites via the poorly characterized AGC-family kinase Ypk3 and the PP1 Phosphatase Glc7, whereas TORC2 regulates phosphorylation of only the N-terminal phosphosite via Ypk1. Cells expressing a nonphosphorylatable variant of Rps6 display a reduced growth rate and a 40S biogenesis defect, but these phenotypes are not observed in cells in which Rps6 kinase activity is compromised. Furthermore, using polysome profiling and ribosome profiling, we failed to uncover a role of Rps6 phosphorylation in either global translation or translation of individual mRNAs. Taking the results together, this work depicts the signaling cascades orchestrating Rps6 phosphorylation in budding yeast, challenges the notion that Rps6 phosphorylation plays a role in translation, and demonstrates that observations made with Rps6 knock-ins must be interpreted cautiously.

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