Mutations in the SAM domain of STE50 differentially influence the MAPK-mediated pathways for mating, filamentous growth and osmotolerance in Saccharomyces cerevisiae

Mol Genet Genomics. 2001 Mar;265(1):102-17. doi: 10.1007/s004380000394.


In Saccharomyces cerevisiae, the MAPKKK Ste11p is involved in three mitogen-activated protein kinase (MAPK) pathways required for mating, filamentous growth and the SHO1-dependent response to hyperosmolarity. All three pathways are also dependent on Ste50p. Ste50p and Ste11p interact constitutively via their N-terminal regions, which include putative SAM domains. Here we show that the interaction of Ste50p and Ste11p is differentially required for modulation of Ste11p function during mating, filamentous growth and the SHO1-dependent response to hyperosmolarity. Two derivatives of Ste50p with mutations in the SAM domain were isolated and characterised. The mutant Ste50 proteins showed reduced binding to Ste11p and a tendency to form homodimers in two-hybrid and in vitro binding assays. Interestingly, these two Ste50p-SAM mutants were associated with increased activation of the mating and filamentous-growth pathways, but a reduction in the SHO1-dependent growth response to hyperosmolarity, relative to the wild-type Ste50p. Moreover, when exposed to hyperosmolarity, these Ste50p-SAM mutants activate genes in the mating (FUS1) and filamentous-growth (FLO11) pathways to higher levels than does the wild type. Thus the Ste50p-Ste11p interaction may differentially modulate the flow of information through the various MAPK-mediated pathways.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Dimerization
  • Fungal Proteins / genetics*
  • Fungal Proteins / metabolism
  • MAP Kinase Kinase Kinases / genetics
  • MAP Kinase Kinase Kinases / metabolism
  • Mating Factor
  • Membrane Glycoproteins
  • Membrane Proteins / metabolism
  • Mitogen-Activated Protein Kinases / metabolism*
  • Molecular Sequence Data
  • Mutation
  • Peptides / physiology
  • Protein Structure, Tertiary
  • Reproduction / physiology
  • Saccharomyces cerevisiae / genetics*
  • Saccharomyces cerevisiae / growth & development
  • Saccharomyces cerevisiae / metabolism
  • Saccharomyces cerevisiae Proteins*
  • Signal Transduction*
  • Two-Hybrid System Techniques
  • Water-Electrolyte Balance


  • FLO11 protein, S cerevisiae
  • FUS1 protein, S cerevisiae
  • Fungal Proteins
  • Membrane Glycoproteins
  • Membrane Proteins
  • Peptides
  • STE50 protein, S cerevisiae
  • Saccharomyces cerevisiae Proteins
  • Mating Factor
  • Mitogen-Activated Protein Kinases
  • MAP Kinase Kinase Kinases
  • Ste11 protein, S cerevisiae