<unk>  (Kirsten rat sarcoma virus) is a gene that provides instructions for making a protein called K-Ras, a part of the RAS/MAPK pathway. The protein relays signals from outside the cell to the cell's nucleus. These signals instruct the cell to grow and divide (proliferate) or to mature and take on specialized functions (differentiate). It is called<unk>  because it was first identified as a viral oncogene in the Kirsten RAt Sarcoma virus. The oncogene identified was derived from a cellular genome, so , when found in a cellular genome, is called a proto-oncogene. The K-Ras protein is a GTPase, a class of enzymes which convert the nucleotide guanosine triphosphate (GTP) into guanosine diphosphate (GDP). In this way the K-Ras protein acts like a switch that is turned on and off by the GTP and GDP molecules. To transmit signals, it must be turned on by attaching (binding) to a molecule of GTP. The K-Ras protein is turned off (inactivated) when it converts the GTP to GDP. When the protein is bound to GDP, it does not relay signals to the cell's nucleus. The gene product of<unk> , the K-Ras protein, was first found as a p21 GTPase. Like other members of the ras subfamily of GTPases, the K-Ras protein is an early player in many signal transduction pathways. K-Ras 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<unk>  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 structures in their C-terminal region and use different mechanisms to localize to cellular membranes, including the plasma membrane.
KRAS
BRAF 
CoWIN
TFM-4AS-1
CDK13
ERCC2
Kras
WRAP53