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About Ste4

  • Ste4 is multiply phosphorylated in a pheromone dependent manner, but these phosphorylations have no detectable effect on response. Li et al. 1998 PMID 9671029
  • Ste5 anf Far1 both bind to Ste4 with homologous RING-H2 domains, suggesting that both Far1 and Ste5 would not be able to simultaneoulsy bind a single molecule of Ste4. Sette et al. 2000 PMID 11071925
  • Sucrose density gradient fractionation suggests that the majority of Ste4 is associated with the plasma membrane and not other internal membranes. Song et al. 1996 PMID 8702760
    • The majority of Ste4 that associates with membranes cosediments with Pma1 (an integral plasma membrane protein marker), suggesting that the majority of Ste4 is associated with the plasma membrane.
    • The authors did not attempt to measure Ste4 in the soluble fraction (not associated with membranes).
  • Renografin density gradient fractionation suggests that about 30% of Ste4 is in the soluble fraction, 40% is associated with the plasma membrane, and 30% is associated with other parts of the pellet. Hirschman et al. 1997 PMID 8995254
    • Pma1 was used as a marker for the plasma membrane fractions.
    • The Renografin concentrations used have an ionic strength equivalent to 0.5 M NaCl. This could disrupt weak protein association with the plasma membrane.

About Ste18

  • Ste18 is farnesylated (prenylated) at C107, and palmitoylated (thioacylated) at C106. Manahan et al. 2000 PMID 10712512
  • Farnesylation at C107 is required for palmitoylation at C106. Manahan et al. 2000 PMID 10712512
  • Defect in palmitoylation results in compromised mating ability, and defect in farnesylation (which causes a defect in palmitoylation as well) results in a sterile phenotype. Manahan et al. 2000 PMID 10712512

About dimer

  • Total amount of G protein per cell was measured by quantitative Western blots and fluorescent quantification to be 10000 per cell. Yi et al. 2003 PMID 12960402
  • Total Ste4:Ste18 concentration of 0.2 nM (which equates to ~7800 moleculse per cell for a 5 μm cell) was used in a model (no source). Hao et al. 2003 PMID 12968019
  • Ste4 and Ste18 are required for eachother's stability. Hirschman et al. 1997 PMID 8995254
    • Deletion of Ste18 results in 50% lower Ste4 levels, and in these cells Ste4 has a half-life of about 90 min.
    • Deletion of Ste4 causes Ste18 levels to drop such that it is barely detectable.


Pheromone/Receptor/G protein interactions
Ste4/Ste18 interaction
Fus3/Gpa1/Ste4 interactions
Ste4:Ste18/Ste5 interactions and Ste5 dimerization/oligomerization
Ste4:Ste18/Ste20 interaction
Protein dilution/synthesis due to cell growth

Species Representation

Molecule Type

Ste4(Gpa1_site, Ste5_site, Ste20_site)


Model Seed

Ste4(Gpa1_site, Ste5_site, Ste20_site) Ste4_tot_conc


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