Rapamycin sensitivity of the Schizosaccharomyces pombe tor2 mutant and organization of two highly phosphorylated TOR complexes by specific and common subunits

Abstract

Nutrients are essential for cell growth and division. Screening of Schizosaccharomyces pombe temperature-sensitive strains led to the isolation of a nutrient-insensitive mutant, tor2-287 . This mutant produces a nitrogen starvation-induced arrest phenotype in rich media, fails to recover from the arrest, and is hypersensitive to rapamycin. The L2048S substitution mutation in the catalytic domain in close proximity to the adenine base of ATP is unique as it is the sole known genetic cause of rapamycin hypersensitivity. Localization of Tor2 was speckled in the vegetative cytoplasm, and both speckled and membranous in the arrested cell cytoplasm. Using mass spectroscopic analysis, we identified six subunits (Tco89, Bit61, Toc1, Tel2, Tti1 and Cka1) that, in addition to the six previously identified subunits (Tor1, Tor2, Mip1/Raptor, Ste20/Rictor, Sin1/ Avo1 and Wat1/Lst8), comprise the TOR complexes (TORCs). All of the subunits so far examined are multiply phosphorylated. Tel2 bound to Tti1 interacts with various phosphatidyl inositol kinase (PIK)-related kinases including Tra1, Tra2 and Rad3, as well as Tor1 and Tor2. Schizosaccharomyces pombe TORCs should thus be functionally redundant and might be broadly regulated through different subunits that are either common or specific to the two TORCs, or even common to various PIK-related kinases. Functional redundancy of the TORCs may explain the rapamycin hypersensitivity of tor2-287 .

Isp7 Is a Novel Regulator of Amino Acid Uptake in the TOR Signaling Pathway

“…Later, it was found that Tor1 is the catalytic subunit of TORC2 while Tor2 is the catalytic subunit of TORC1. TORC1 also contains the protein Mip1 (raptor in humans), and TORC2 also contains the proteins Ste20 (rictor in humans) and Sin1 (mSin1 in humans) (13)(14)(15)(16)(17)(18)(19)(20). TORC1 is essential under normal growth conditions and plays major roles in the control of cellular growth, possibly in response to nitrogen availability (17,(20)(21)(22)(23)(24)(25).…”

Germ Cell Apoptosis and DNA Damage Responses

“…Genome instability also occurs in clk-2 mutant germlines, but strong alleles lead to a late G2-like cell cycle arrest. Subsequent studies on mammalian and yeast CLK-2 orthologs, referred to as TEL2 in yeasts, established that CLK-2/TEL2 is required for the full activation of all PIKKs-type protein kinases, a class of protein kinases that includes ATM/ atm-1 and ATL-1, thus explaining checkpoint-signalling phenotypes (Hayashi et al 2007 ;Kanoh and Yanagida 2007 ;Hurov et al 2010 ;Takai et al 2010 ;Kaizuka et al 2010 ) . The current model suggests that CLK-2/TEL2 might have a chaperonlike function required for the full activation of those kinases (Horejsi et al 2010 ) .…”

TORC2 Is Required to Maintain Genome Stability during S Phase in Fission Yeast

“…These were numbered based on their order of discovery. Later, it was found that Tor1 interacts with Ste20 (Rictor) and Sin1 to form TORC2, whereas Tor2 interacts with Mip1 (Raptor) to form TORC1 (10,11). As in human cells, S. pombe TORC1 is negatively regulated by the TSC complex (12,13).…”