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 SoS, or Son of Sevenless, is an example of a guanine nucleotide exchange factor (GEF) needed for the activation of GTPase found on Ras proteins, a group of monomeric G proteins. SoS is involved in the transduction of a signal and is required to relay the signal down intracellular signalling pathways[1]. As SoS is activating  the Ras-GTPase, it is an example of a positive regulator and does this by triggering the release of GDP from the GTPase, allowing it to take up GTP[2] Without Son of Sevenless, monomeric G proteins cannot exchange GDP for GTP as its own intrinsic catalytic activity is weak and so must bind to SoS. Despite this, the adaptor protein Grb2 must first bind to SoS, which gives SoS the ability to initiate the take up of GTP. This occurs once epidermal growth factors in the extracellular space, acting as signal molecules, bind to receptor tyrosine kinases (RTKs) which stimulates tyrosine residues in the cytoplasmic domain of the RTK to activate via autophosphorylation[3].


  1. This is a reference to Alberts B, Johnson A, Lewis J, Morgan D, Raff M, Roberts K, Walter P. Molecular Biology of The Cell. 6th Ed, New York: Garland Science Taylor and Francis Group. 2015.
  2. This is a reference to José M. Rojas, José Luis Oliva, Eugenio Santos. Genes & Cancer. Mammalian Son of Sevenless Guanine Nucleotide Exchange Factors: Old Concepts and New Perspectives. 2011: Vol 2, Issue 3, pages 298-305.
  3. This is a reference to B Margolis, EY Skolnik. Journal of the American Society of Nephrology. Activation of Ras by receptor tyrosine kinases. 1994; Vol 5, Issue6; 1288-1299
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