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Gene Review

TOK1  -  Tok1p

Saccharomyces cerevisiae S288c

Synonyms: DUK1, J0911, Outward-rectifier potassium channel TOK1, Two-domain outward rectifier K(+) channel YORK, YJL093C, ...
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Disease relevance of TOK1


High impact information on TOK1

  • Osmotic stress activates Hog1 MAP kinase, which phosphorylates at least two proteins located at the plasma membrane, the Nha1 Na+/H+ antiporter and the Tok1 potassium channel [2].
  • Recently, external K1 toxin was shown to directly activate TOK1 channels in the plasma membranes of sensitive yeast cells, leading to excess potassium flux and cell death [3].
  • Here, a mechanism by which killer cells resist their own toxin is shown: internal toxin inhibits TOK1 channels and suppresses activation by external toxin [3].
  • K1 toxin acts in the absence of other viral or yeast products: toxin synthesized from a cDNA increases open probability of single TOK1 channels (via reversible destabilization of closed states) whether channels are studied in yeast cells or X. laevis oocytes [4].
  • Random mutagenesis reveals a region important for gating of the yeast K+ channel Ykc1 [5].

Biological context of TOK1

  • The current through TOK1 (YKC1), the outward-rectifying K+ channel in Saccharomyces cerevisiae, was amplified by expressing TOK1 from a plasmid driven by a strong constitutive promoter [6].
  • This trk1Delta trk2Delta double mutant hyperexpressing the TOK1 transgene had a higher internal K+ content than one expressing the empty plasmid [6].
  • We have shown that the presence of the Tok1 channel strongly influences membrane potential: deletion of the TOK1 gene results in significant plasma membrane depolarization, whereas strains overexpressing the TOK1 gene are hyperpolarized [7].
  • Non-targeted mutagenesis studies of the yeast K(+) channel, TOK1, have led to identification of functional domains common to other cation channels as well as those so far not found in other channels [8].
  • These and additional results indicate that external K+ acts as a ligand to inactivate the TOK1p channel, and they implicate a gating process mediated by a single cation binding site within the membrane electric field, but distinct from the permeation pathway [9].

Anatomical context of TOK1


Associations of TOK1 with chemical compounds

  • In contrast, the nonanesthetic 1,2-dichlorohexafluorocyclobutane did not potentiate TOK1 currents in concentrations up to five times the MAC value predicted by the Meyer-Overton hypothesis based on oil/gas partition coefficients [12].
  • RESULTS: Studies with two-electrode voltage clamp at room temperature showed that halothane, isoflurane, and desflurane increased TOK1 outward currents by 48-65% in barium Frog Ringer's perfusate [12].
  • These PP mutations specifically caused marked defects in the 'C1' states, a set of interrelated closed states that Ykc1 enters and exits at rates of tens to hundreds of milliseconds [5].
  • In the yeast potassium channel, Tok1p, the external ring of aspartate residues modulates both gating and conductance [13].
  • Cells carrying the duk1 delta 1::HIS disruption in addition to a chimeric gene comprising DUK1 behind the GAL1 promoter showed outward currents when grown in galactose, but not when grown in glucose [11].

Other interactions of TOK1

  • Characterization of potassium transport in wild-type and isogenic yeast strains carrying all combinations of trk1, trk2 and tok1 null mutations [14].
  • Deletion mutants of the two unknown genes J0909 and J0911 are viable [15].


  1. Deletions of SKY1 or PTK2 in the Saccharomyces cerevisiae trk1Deltatrk2Delta mutant cells exert dual effect on ion homeostasis. Erez, O., Kahana, C. Biochem. Biophys. Res. Commun. (2002) [Pubmed]
  2. MAP kinase-mediated stress relief that precedes and regulates the timing of transcriptional induction. Proft, M., Struhl, K. Cell (2004) [Pubmed]
  3. Immunity to K1 killer toxin: internal TOK1 blockade. Sesti, F., Shih, T.M., Nikolaeva, N., Goldstein, S.A. Cell (2001) [Pubmed]
  4. A molecular target for viral killer toxin: TOK1 potassium channels. Ahmed, A., Sesti, F., Ilan, N., Shih, T.M., Sturley, S.L., Goldstein, S.A. Cell (1999) [Pubmed]
  5. Random mutagenesis reveals a region important for gating of the yeast K+ channel Ykc1. Loukin, S.H., Vaillant, B., Zhou, X.L., Spalding, E.P., Kung, C., Saimi, Y. EMBO J. (1997) [Pubmed]
  6. Potassium uptake through the TOK1 K+ channel in the budding yeast. Fairman, C., Zhou, X., Kung, C. J. Membr. Biol. (1999) [Pubmed]
  7. Measurements of plasma membrane potential changes in Saccharomyces cerevisiae cells reveal the importance of the Tok1 channel in membrane potential maintenance. Maresova, L., Urbankova, E., Gaskova, D., Sychrova, H. FEMS Yeast Res. (2006) [Pubmed]
  8. The carboxyl tail forms a discrete functional domain that blocks closure of the yeast K+ channel. Loukin, S.H., Lin, J., Athar, U., Palmer, C., Saimi, Y. Proc. Natl. Acad. Sci. U.S.A. (2002) [Pubmed]
  9. Extracellular K+ and Ba2+ mediate voltage-dependent inactivation of the outward-rectifying K+ channel encoded by the yeast gene TOK1. Vergani, P., Miosga, T., Jarvis, S.M., Blatt, M.R. FEBS Lett. (1997) [Pubmed]
  10. Physiological characterization of the yeast plasma membrane outward rectifying K+ channel, DUK1 (TOK1), in situ. Bertl, A., Bihler, H., Reid, J.D., Kettner, C., Slayman, C.L. J. Membr. Biol. (1998) [Pubmed]
  11. The S. cerevisiae outwardly-rectifying potassium channel (DUK1) identifies a new family of channels with duplicated pore domains. Reid, J.D., Lukas, W., Shafaatian, R., Bertl, A., Scheurmann-Kettner, C., Guy, H.R., North, R.A. Recept. Channels (1996) [Pubmed]
  12. TOK1 is a volatile anesthetic stimulated K+ channel. Gray, A.T., Winegar, B.D., Leonoudakis, D.J., Forsayeth, J.R., Yost, C.S. Anesthesiology (1998) [Pubmed]
  13. In the yeast potassium channel, Tok1p, the external ring of aspartate residues modulates both gating and conductance. Roller, A., Natura, G., Bihler, H., Slayman, C.L., Eing, C., Bertl, A. Pflugers Arch. (2005) [Pubmed]
  14. Characterization of potassium transport in wild-type and isogenic yeast strains carrying all combinations of trk1, trk2 and tok1 null mutations. Bertl, A., Ramos, J., Ludwig, J., Lichtenberg-Fraté, H., Reid, J., Bihler, H., Calero, F., Martínez, P., Ljungdahl, P.O. Mol. Microbiol. (2003) [Pubmed]
  15. Sequence and function analysis of a 9.46 kb fragment of Saccharomyces cerevisiae chromosome X. Miosga, T., Witzel, A., Zimmermann, F.K. Yeast (1994) [Pubmed]
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