K-ras, V-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog, is a protein that in humans is encoded by the KRAS gene. Like other members of the Ras family, the K-ras protein is a GTPase and is an early player in many signal transduction pathways. K-ras is usually tethered to cell membranes because of the presence of an isoprenyl group on its C-terminus. The K-ras gene spans 38 kb and contains 4 exons. By in situ hybridization, the K-ras gene is mapped to chromosome 12p12.1-p11.1. K-ras acts as a molecular on/off switch. Once it is turned on it recruits and activates proteins necessary for the propagation of growth factor and other receptors' signal, such as c-Raf and PI 3-kinase. K-ras binds to GTP in the active state and possesses an intrinsic enzymatic activity which cleaves the terminal phosphate of the nucleotide converting it to GDP