p21 RAS:GTP p21 RAS:GDP Activation of RAS by p-KIT bound SOS1 Authored: Garapati, P V, 2011-07-11 Edited: Garapati, P V, 2011-07-11 Once recruited to the membrane in response to c-Kit stimulation, Son of sevenless (SOS1) activates the small GTPase protein Ras. SOS1 is a dual specificity guanine nucleotide exchange factor (GEF) that regulates both Ras and Rho family GTPases. SOS1 activates Ras by binding which induces a conformational change that causes the exchange of GDP with GTP. Ras proteins are membrane-bound GTPases that regulate crucial cellular processes such as growth, proliferation and differentiation. Active Ras-GTP stimulates multiple effector proteins such as Raf-1, which induce a variety of cellular responses, including initiation of mitogen activated protein kinase (MAPK) cascade signaling. Pubmed1371879 Pubmed16129412 Pubmed16483568 Pubmed17052120 Pubmed1721591 Reactome Database ID Release 431433471 Reactome, http://www.reactome.org ReactomeREACT_111091 Reviewed: Rönnstrand, L, 2011-08-22