Cross-talk between ammonium transporters in yeast and interference by the soybean SAT1 protein

Mol Microbiol. 2000 Jan;35(2):378-85. doi: 10.1046/j.1365-2958.2000.01704.x.


Ammonium uptake in the yeast Saccharomyces cerevisiae involves three membrane transporters (Mep1, -2 and -3) belonging to an evolutionarily conserved protein family that also includes the rhesus (Rh) blood group polypeptides of erythrocytes. We show here that, in the 26972c mutant defective in NH4+ transport, the Mep1 protein carrying an amino acid substitution in its cytoplasmic C-terminus trans-inhibits the closely related Mep3 protein. The same mutation introduced into Mep3 leads to loss of transport activity and this inactive form also trans-inhibits native Mep3. Inhibition of Mep3 is post-translational and can be overcome by overexpression. These results are consistent with a direct interaction between Mep proteins, as is the case for the Rh polypeptides. The soybean GmSAT1 gene, recently cloned for its ability to complement the NH4+ transport defect of strain 26972c, has been described as an NH4+ channel protein involved in the transfer of fixed nitrogen from the bacteroid to the host plant. We show here that GmSAT1 contains a sequence homologous to the DNA-binding domain of basic helix-loop-helix (bHLH) transcription factors. We also show that GmSAT1 restores NH4+ uptake in the yeast mutant by interfering with the inhibition of Mep3. Our results are not consistent with a direct role of GmSAT1 in ammonium transport.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Biological Transport
  • Carrier Proteins / chemistry
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism*
  • Cation Transport Proteins*
  • Culture Media
  • Electrophoresis, Polyacrylamide Gel
  • Fungal Proteins / genetics
  • Fungal Proteins / metabolism*
  • Gene Expression Regulation, Fungal
  • Helix-Loop-Helix Motifs
  • Humans
  • Immunoblotting
  • Molecular Sequence Data
  • Mutation
  • Plasmids / genetics
  • Quaternary Ammonium Compounds / metabolism*
  • Saccharomyces cerevisiae / genetics
  • Saccharomyces cerevisiae / growth & development
  • Saccharomyces cerevisiae / metabolism*
  • Saccharomyces cerevisiae Proteins*
  • Sequence Alignment
  • Soybean Proteins*


  • Carrier Proteins
  • Cation Transport Proteins
  • Culture Media
  • Fungal Proteins
  • MEP1 protein, S cerevisiae
  • MEP2 protein, S cerevisiae
  • MEP3 protein, S cerevisiae
  • Quaternary Ammonium Compounds
  • SAT1 protein, glycine max
  • Saccharomyces cerevisiae Proteins
  • Soybean Proteins