Tyrosine-protein kinase KIT (cKIT) also known as CD117 or mast/stem cell growth factor receptor (SCFR) is encoded by the proto-oncogene c-KIT gene. KIT is a receptor tyrosine kinase type III, which binds to stem cell factor, also known as "steel factor" or "c-kit ligand". Like other members of the receptor tyrosine kinase III family, KIT consists of an extracellular domain, a transmembrane domain, a juxtamembrane domain, and an intracellular tyrosine kinase domain. The extracellular domain is composed of five immunoglobulin-like domains, and the ligand stem cell factor binds via the second and third immunoglobulin domains. When KIT binds to stem cell factor (SCF) it forms a dimer that activates its intrinsic tyrosine kinase activity, that in turn phosphorylates and activates signal transduction molecules that propagate the signal in the cell.