Sch9 partially mediates TORC1 signaling to control ribosomal RNA synthesis

Cell Cycle. 2009 Dec 15;8(24):4085-90. doi: 10.4161/cc.8.24.10170. Epub 2009 Dec 25.


TORC1 is a central regulator of ribosomal RNA synthesis. Here we report that Sch9 partially mediates TORC1 signaling to regulate Pol I- and Pol III-dependent transcription. Mechanistically, Sch9 is involved in hyperphosphorylation and cytoplasmic localization of Maf1, and for optimal synthesis of rRNAs and tRNAs. Interestingly, sch9Delta does not affect Maf1 basal phosphorylation and nucleolar localization. In addition, TORC1 is still capable of regulating rRNAs and tRNAs in the absence of Sch9. Moreover, the hyperactive Sch9(2D3E) mutant does not confer significant rapamycin resistance in cell growth. Together, these observations indicate that Sch9 is involved in optimal regulation of ribosome biogenesis by TORC1, but is dispensable for the essential aspects of ribosome biogenesis and cell growth, suggesting that TORC1 controls cell growth through Sch9-dependent and independent mechanisms.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Gene Expression Regulation, Fungal / genetics
  • Intracellular Signaling Peptides and Proteins / genetics*
  • Intracellular Signaling Peptides and Proteins / metabolism
  • Macromolecular Substances / metabolism
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism
  • Mutation / genetics
  • Phosphatidylinositol 3-Kinases / genetics*
  • Phosphatidylinositol 3-Kinases / metabolism
  • Protein-Serine-Threonine Kinases / genetics*
  • Protein-Serine-Threonine Kinases / metabolism
  • RNA Polymerase I / genetics
  • RNA, Ribosomal / biosynthesis*
  • RNA, Transfer / genetics
  • Saccharomyces cerevisiae / genetics*
  • Saccharomyces cerevisiae / metabolism
  • Saccharomyces cerevisiae Proteins / genetics*
  • Saccharomyces cerevisiae Proteins / metabolism
  • Signal Transduction / genetics
  • Transcription Factors / genetics
  • Transcriptional Activation / genetics


  • Intracellular Signaling Peptides and Proteins
  • Kog1 protein, S cerevisiae
  • LST8 protein, S cerevisiae
  • MAF1 protein, S cerevisiae
  • Macromolecular Substances
  • Membrane Proteins
  • RNA, Ribosomal
  • Saccharomyces cerevisiae Proteins
  • Transcription Factors
  • RNA, Transfer
  • TOR1 protein, S cerevisiae
  • Protein-Serine-Threonine Kinases
  • SCH9 protein, S cerevisiae
  • RNA Polymerase I