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.