Fission yeast TOR complex 1 phosphorylates Psk1 through an evolutionarily conserved interaction mediated by the TOS motif

J Cell Sci. 2021 Oct 1;134(19):jcs258865. doi: 10.1242/jcs.258865. Epub 2021 Oct 12.


TOR complex 1 (TORC1) is a multi-subunit protein kinase complex that controls cellular growth in response to environmental cues. The regulatory subunits of mammalian TORC1 (mTORC1) include RAPTOR (also known as RPTOR), which recruits mTORC1 substrates, such as S6K1 (also known as RPS6KB1) and 4EBP1 (EIF4EBP1), by interacting with their TOR signaling (TOS) motif. Despite the evolutionary conservation of TORC1, no TOS motif has been described in lower eukaryotes. In the present study, we show that the fission yeast S6 kinase Psk1 contains a TOS motif that interacts with Mip1, a RAPTOR ortholog. The TOS motif in Psk1 resembles those in mammals, including the conserved phenylalanine and aspartic acid residues essential for the Mip1 interaction and TORC1-dependent phosphorylation of Psk1. The binding of the TOS motif to Mip1 is dependent on Mip1 Tyr-533, whose equivalent in RAPTOR is known to interact with the TOS motif in their co-crystals. Furthermore, we utilized the mip1-Y533A mutation to screen the known TORC1 substrates in fission yeast and successfully identified Atg13 as a novel TOS-motif-containing substrate. These results strongly suggest that the TOS motif represents an evolutionarily conserved mechanism of the substrate recognition by TORC1.

Keywords: Fission yeast; Mip1; TOR complex 1; TORC1; TOS motif.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Mechanistic Target of Rapamycin Complex 1 / genetics
  • Mechanistic Target of Rapamycin Complex 1 / metabolism
  • Phosphorylation
  • Regulatory-Associated Protein of mTOR
  • Schizosaccharomyces pombe Proteins* / genetics
  • Schizosaccharomyces pombe Proteins* / metabolism
  • Schizosaccharomyces* / genetics
  • Schizosaccharomyces* / metabolism


  • Regulatory-Associated Protein of mTOR
  • Schizosaccharomyces pombe Proteins
  • Mechanistic Target of Rapamycin Complex 1