Search tips
Search criteria

Results 1-6 (6)

Clipboard (0)

Select a Filter Below

more »
Year of Publication
Document Types
1.  Phosphorylation of the TOR ATP binding domain by AGC kinase constitutes a novel mode of TOR inhibition 
The Journal of Cell Biology  2013;203(4):595-604.
AGC kinase–mediated phosphorylation of the TOR kinase reduces its activity and results in physiologically significant changes in TOR signalling in both yeast and human cells.
TOR (target of rapamycin) signaling coordinates cell growth, metabolism, and cell division through tight control of signaling via two complexes, TORC1 and TORC2. Here, we show that fission yeast TOR kinases and mTOR are phosphorylated on an evolutionarily conserved residue of their ATP-binding domain. The Gad8 kinase (AKT homologue) phosphorylates fission yeast Tor1 at this threonine (T1972) to reduce activity. A T1972A mutation that blocked phosphorylation increased Tor1 activity and stress resistance. Nitrogen starvation of fission yeast inhibited TOR signaling to arrest cell cycle progression in G1 phase and promoted sexual differentiation. Starvation and a Gad8/T1972-dependent decrease in Tor1 (TORC2) activity was essential for efficient cell cycle arrest and differentiation. Experiments in human cell lines recapitulated these yeast observations, as mTOR was phosphorylated on T2173 in an AKT-dependent manner. In addition, a T2173A mutation increased mTOR activity. Thus, TOR kinase activity can be reduced through AGC kinase–controlled phosphorylation to generate physiologically significant changes in TOR signaling.
PMCID: PMC3840928  PMID: 24247430
2.  Extending the Schizosaccharomyces pombe Molecular Genetic Toolbox 
PLoS ONE  2014;9(5):e97683.
Targeted alteration of the genome lies at the heart of the exploitation of S. pombe as a model system. The rate of analysis is often determined by the efficiency with which a target locus can be manipulated. For most loci this is not a problem, however for some loci, such as fin1+, rates of gene targeting below 5% can limit the scope and scale of manipulations that are feasible within a reasonable time frame. We now describe a simple modification of transformation procedure for directing integration of genomic sequences that leads to a 5-fold increase in the transformation efficiency when antibiotic based dominant selection markers are used. We also show that removal of the pku70+ and pku80+ genes, which encode DNA end binding proteins required for the non-homologous end joining DNA repair pathway, increases the efficiency of gene targeting at fin1+ to around 75–80% (a 16-fold increase). We describe how a natMX6/rpl42+ cassette can be used for positive and negative selection for integration at a targeted locus. To facilitate the evaluation of the impact of a series of mutations on the function of a gene of interest we have generated three vector series that rely upon different selectable markers to direct the expression of tagged/untagged molecules from distinct genomic integration sites. pINTL and pINTK vectors use ura4+ selection to direct disruptive integration of leu1+ and lys1+ respectively, while pINTH vectors exploit nourseothricin resistance to detect the targeted disruption of a hygromycin B resistance conferring hphMX6 cassette that has been integrated on chromosome III. Finally, we have generated a series of multi-copy expression vectors that use resistance to nourseothricin or kanamycin/G418 to select for propagation in prototrophic hosts. Collectively these protocol modifications and vectors extend the versatility of this key model system.
PMCID: PMC4029729  PMID: 24848109
3.  Torin1-mediated TOR kinase inhibition reduces Wee1 levels and advances mitotic commitment in fission yeast and HeLa cells 
Journal of Cell Science  2014;127(6):1346-1356.
The target of rapamycin (TOR) kinase regulates cell growth and division. Rapamycin only inhibits a subset of TOR activities. Here we show that in contrast to the mild impact of rapamycin on cell division, blocking the catalytic site of TOR with the Torin1 inhibitor completely arrests growth without cell death in Schizosaccharomyces pombe. A mutation of the Tor2 glycine residue (G2040D) that lies adjacent to the key Torin-interacting tryptophan provides Torin1 resistance, confirming the specificity of Torin1 for TOR. Using this mutation, we show that Torin1 advanced mitotic onset before inducing growth arrest. In contrast to TOR inhibition with rapamycin, regulation by either Wee1 or Cdc25 was sufficient for this Torin1-induced advanced mitosis. Torin1 promoted a Polo and Cdr2 kinase-controlled drop in Wee1 levels. Experiments in human cell lines recapitulated these yeast observations: mammalian TOR (mTOR) was inhibited by Torin1, Wee1 levels declined and mitotic commitment was advanced in HeLa cells. Thus, the regulation of the mitotic inhibitor Wee1 by TOR signalling is a conserved mechanism that helps to couple cell cycle and growth controls.
PMCID: PMC3953821  PMID: 24424027
HeLa; S. pombe; TOR; Torin1; Wee1
4.  TORC2 and the AGC kinase Gad8 regulate phosphorylation of the ribosomal protein S6 in fission yeast 
Biology Open  2012;1(9):884-888.
TOR (Target Of Rapamycin) signalling coordinates cell growth and division in response to changes in the nutritional environment of the cell. TOR kinases form two distinct complexes: TORC1 and TORC2. In mammals, the TORC1 controlled S6K1 kinase phosphorylates the ribosomal protein S6 thereby co-ordinating cell size and nutritional status. We show that the Schizosaccharomyces pombe AGC kinase Gad8 co-immunoprecipitates with the ribosomal protein S6 (Rps6) and regulates its phosphorylation status. It has previously been shown that Gad8 is phosphorylated by TORC2. Consistent with this, we find that TORC2 as well as TORC1 modulates Rps6 phosphorylation. Therefore, S6 phosphorylation in fission yeast actually represents a read-out of the combined activities of TORC1 and TORC2. In contrast, we find that the in vivo phosphorylation status of Maf1 (a repressor of RNA polymerase III) specifically correlates with TORC1 activity.
PMCID: PMC3507231  PMID: 23213482
Gad8; Maf1; S6; S6K; TOR; S. pombe
5.  FH3, A Domain Found in Formins, Targets the Fission Yeast Formin Fus1 to the Projection Tip During Conjugation  
The Journal of Cell Biology  1998;141(5):1217-1228.
Formins are involved in diverse aspects of morphogenesis, and share two regions of homology: FH1 and FH2. We describe a new formin homology region, FH3. FH3 is an amino-terminal domain that differs from the Rho binding site identified in Bni1p and p140mDia. The Schizosaccharomyces pombe formin Fus1 is required for conjugation, and is localized to the projection tip in cells of mating pairs. We replaced genomic fus1+ with green fluorescent protein (GFP)- tagged versions that lacked either the FH1, FH2, or FH3 domain. Deletion of any FH domain essentially abolished mating. FH3, but neither FH1 nor FH2, was required for Fus1 localization. An FH3 domain–GFP fusion protein localized to the projection tips of mating pairs. Thus, the FH3 domain alone can direct protein localization. The FH3 domains of both Fus1 and the S. pombe cytokinesis formin Cdc12 were able to localize GFP to the spindle pole body in half of the late G2 cells in a vegetatively growing population. Expression of both FH3-GFP fusions also affected cytokinesis. Overexpression of the spindle pole body component Sad1 altered the distribution of both Sad1 and the FH3-GFP domain. Together these data suggest that proteins at multiple sites can interact with FH3 domains.
PMCID: PMC2137179  PMID: 9606213
6.  Plo1 Kinase Recruitment to the Spindle Pole Body and Its Role in Cell Division in Schizosaccharomyces pombe 
Molecular Biology of the Cell  1999;10(8):2771-2785.
Polo kinases execute multiple roles during cell division. The fission yeast polo related kinase Plo1 is required to assemble the mitotic spindle, the prophase actin ring that predicts the site for cytokinesis and for septation after the completion of mitosis (Ohkura et al., 1995; Bahler et al., 1998). We show that Plo1 associates with the mitotic but not interphase spindle pole body (SPB). SPB association of Plo1 is the earliest fission yeast mitotic event recorded to date. SPB association is strong from mitotic commitment to early anaphase B, after which the Plo1 signal becomes very weak and finally disappears upon spindle breakdown. SPB association of Plo1 requires mitosis-promoting factor (MPF) activity, whereas its disassociation requires the activity of the anaphase-promoting complex. The stf1.1 mutation bypasses the usual requirement for the MPF activator Cdc25 (Hudson et al., 1990). Significantly, Plo1 associates inappropriately with the interphase SPB of stf1.1 cells. These data are consistent with the emerging theme from many systems that polo kinases participate in the regulation of MPF to determine the timing of commitment to mitosis and may indicate that pole association is a key aspect of Plo1 function. Plo1 does not associate with the SPB when septation is inappropriately driven by deregulation of the Spg1 pathway and remains SPB associated if septation occurs in the presence of a spindle. Thus, neither Plo1 recruitment to nor its departure from the SPB are required for septation; however, overexpression of plo1+ activates the Spg1 pathway and causes transient Cdc7 recruitment to the SPB and multiple rounds of septation.
PMCID: PMC25513  PMID: 10436027

Results 1-6 (6)