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Gene Review

TRK2  -  Trk2p

Saccharomyces cerevisiae S288c

Synonyms: Low-affinity potassium transport protein, RPD2, YKR050W
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Disease relevance of TRK2

  • Cells deficient for both high and low affinity K+ transport (trk1 delta trk2) exhibit hypersensitivity to low extracellular pH that can be suppressed by high concentrations of K+ but not Na+ [1].

High impact information on TRK2

  • The URS1-TRK2 sequence (5'-AGCCGCACG-3') shares six nucleotides with the ubiquitous URS1 element (5'-AGCCGCCGA-3'), and the protein species binding URS1-CAR1 (URSF) is capable of binding URS1-TRK2 in vitro [2].
  • The present study uses whole-cell patch-clamp experiments to show that yeast strains which grow poorly on submillimolar K+ due to the deletion of two K(+)-transporter genes (TRK1 and TRK2) are in fact missing a prominent K+ inward current present in wild-type cells [3].
  • Among suppressors of the K+ transport defect in trk1 delta trk2 delta cells, we have identified members of the sugar transporter gene superfamily [4].
  • TRK2 shares 55% amino acid sequence identity with TRK1 [5].
  • Additional observations showed (i). membrane-associated Trk2p to lie in proteolipid rafts; (ii). significant tagged protein, expressed from the plasmid, to be sequestered in cytoplasmic vesicular-tubular clusters; and (iii). suppression of such clusters by yeast growth in 5-10% glycerol [6].

Biological context of TRK2

  • In cells containing a deletion of TRK1, transcription levels of TRK2 are extremely low and are limiting for growth in media containing low levels of K+ (Trk- phenotype) [7].
  • TRK2 is nonessential in TRK1 or trk1 delta haploid cells [5].
  • On the basis of the latter analyses, it is proposed that Trk1p and Trk2p are involved in the control of the membrane potential, preventing excessive hyperpolarizations [8].
  • In view of background knowledge on K+ transport related to Trk2p, the new results suggest that the K+ status of yeast cells modulates both the kinetics of Trk2p-mediated transport and the identity of ions involved [9].
  • The highest rate of ATP hydrolysis in vitro was found with the trk1 delta trk2 delta mutant where glucose-, as well as KCl-induced acidification were lowest [10].

Anatomical context of TRK2

  • It appears that, in addition to the H+ export by the PMA1-coded plasma membrane H(+)-ATPase, at least three different univalent-cation involving activities are present: the high-affinity transport system for K+ (TRK1), another system (possibly TRK2) with different responses to K+ and Rb+, vs. Tl+, and an active system for K+ export [11].

Associations of TRK2 with chemical compounds

  • TKHp, the product of SpTRK exhibits high homology to TRK1 and TRK2 of Saccharomyces cerevisiae as well as to HKT1 of Triticum aestivum, but is not related to HAK1 of another ascomycete, Schwanniomyces occidentalis, suggesting that different routes for potassium uptake evolved independently [12].
  • Growth of trk1 Delta trk2 Delta cells is also inhibited by lithium and ammonium; however, these ions do not inhibit NSC1, but instead enter yeast cells via NSC1 [13].
  • Factors which suppress NSC1-mediated inward currents and inhibit growth of trk1 Delta trk2 Delta cells include (i) elevating extracellular calcium over the range of 10 microM-10 mM, (ii) lowering extracellular pH over the range 7.5-4, (iii) blockade of NSC1 by hygromycin B, and (iv) to a lesser extent by TEA(+) [13].

Regulatory relationships of TRK2

  • The N. crassa TRK1 and HAK1 transporters expressed by the corresponding cDNAs in a trk1 delta trk2 delta mutant of S. cerevisiae exhibited a high affinity for Rb+ and K+ [14].

Other interactions of TRK2

  • Here we show that growth of a Deltatrk1Deltasin3 double mutant, under K+-limiting conditions or at low pH, is Trk2p-dependent, and by Northern blot analysis we demonstrate that deletion of SIN3 results in transcriptional derepression of TRK2 [15].
  • We now report a function for the non-activated form of Snf1: the regulation of the Trk high-affinity potassium transporter, encoded by the TRK1 and TRK2 genes [16].


  1. TRK2 is required for low affinity K+ transport in Saccharomyces cerevisiae. Ko, C.H., Buckley, A.M., Gaber, R.F. Genetics (1990) [Pubmed]
  2. Identification of essential nucleotides in an upstream repressing sequence of Saccharomyces cerevisiae by selection for increased expression of TRK2. Vidal, M., Buckley, A.M., Yohn, C., Hoeppner, D.J., Gaber, R.F. Proc. Natl. Acad. Sci. U.S.A. (1995) [Pubmed]
  3. Use of Saccharomyces cerevisiae for patch-clamp analysis of heterologous membrane proteins: characterization of Kat1, an inward-rectifying K+ channel from Arabidopsis thaliana, and comparison with endogeneous yeast channels and carriers. Bertl, A., Anderson, J.A., Slayman, C.L., Gaber, R.F. Proc. Natl. Acad. Sci. U.S.A. (1995) [Pubmed]
  4. Roles of multiple glucose transporters in Saccharomyces cerevisiae. Ko, C.H., Liang, H., Gaber, R.F. Mol. Cell. Biol. (1993) [Pubmed]
  5. TRK1 and TRK2 encode structurally related K+ transporters in Saccharomyces cerevisiae. Ko, C.H., Gaber, R.F. Mol. Cell. Biol. (1991) [Pubmed]
  6. Epitope tagging of the yeast K(+) carrier Trk2p demonstrates folding that is consistent with a channel-like structure. Zeng, G.F., Pypaert, M., Slayman, C.L. J. Biol. Chem. (2004) [Pubmed]
  7. RPD3 encodes a second factor required to achieve maximum positive and negative transcriptional states in Saccharomyces cerevisiae. Vidal, M., Gaber, R.F. Mol. Cell. Biol. (1991) [Pubmed]
  8. Ectopic potassium uptake in trk1 trk2 mutants of Saccharomyces cerevisiae correlates with a highly hyperpolarized membrane potential. Madrid, R., Gómez, M.J., Ramos, J., Rodríguez-Navarro, A. J. Biol. Chem. (1998) [Pubmed]
  9. The presumed potassium carrier Trk2p in Saccharomyces cerevisiae determines an H+-dependent, K+-independent current. Bihler, H., Gaber, R.F., Slayman, C.L., Bertl, A. FEBS Lett. (1999) [Pubmed]
  10. Different sources of acidity in glucose-elicited extracellular acidification in the yeast Saccharomyces cerevisiae. Lapathitis, G., Kotyk, A. Biochem. Mol. Biol. Int. (1998) [Pubmed]
  11. Univalent cation fluxes in yeast. Lapathitis, G., Kotyk, A. Biochem. Mol. Biol. Int. (1998) [Pubmed]
  12. The SpTRK gene encodes a potassium-specific transport protein TKHp in Schizosaccharomyces pombe. Lichtenberg-Fraté, H., Reid, J.D., Heyer, M., Höfer, M. J. Membr. Biol. (1996) [Pubmed]
  13. Low-affinity potassium uptake by Saccharomyces cerevisiae is mediated by NSC1, a calcium-blocked non-specific cation channel. Bihler, H., Slayman, C.L., Bertl, A. Biochim. Biophys. Acta (2002) [Pubmed]
  14. Cloning of two genes encoding potassium transporters in Neurospora crassa and expression of the corresponding cDNAs in Saccharomyces cerevisiae. Haro, R., Sainz, L., Rubio, F., Rodríguez-Navarro, A. Mol. Microbiol. (1999) [Pubmed]
  15. The yeast potassium transporter TRK2 is able to substitute for TRK1 in its biological function under low K and low pH conditions. Michel, B., Lozano, C., Rodríguez, M., Coria, R., Ramírez, J., Peña, A. Yeast (2006) [Pubmed]
  16. A role for the non-phosphorylated form of yeast Snf1: tolerance to toxic cations and activation of potassium transport. Portillo, F., Mulet, J.M., Serrano, R. FEBS Lett. (2005) [Pubmed]
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