KRAS is proto-oncogene corresponding to the oncogene first identified in Kirsten rat sarcoma virus and the gene product was first found as a p21 GTPase.
The normal KRAS protein performs an essential function in normal tissue signaling, and the mutation of a KRAS gene is an essential step in the development of many cancers.
Like other members of the ras subfamily, the KRAS protein is a GTPase and is an early player in many signal transduction pathways. KRAS is usually tethered to cell membranes because of the presence of an isoprene group on its C-terminus. There are two protein products of the KRAS gene in mammalian cells that result from the use of alternative exon 4 (exon 4A and 4B respectively): K-Ras4A and K-Ras4B, these proteins have different structure in their C-terminal region and use different mechanisms to localize to cellular membranes including the plasma membrane.