A family of oncogenes that encode for GTPases (enzymes located at the plasma membrane or in the cytoplasm). They were first identified as the transforming genes in the Harvey sarcoma virus (H- or Ha-ras) and the Kirsten sarcoma virus (K- or Ki-ras).

From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.