A family of oncogenes, first identified as transforming genes of Harvey and Kirsten murine sarcoma viruses. (‘ras’ from rat sarcoma because the murine Harvey virus obtained its transforming gene during passage in a rat). The gene product is a GTP-binding protein (p21ras) with GTPase activity, that resembles regulatory G-proteins. See ras-like GTPases. The KRAS, HRAS, and NRAS genes encode the human cellular homologues of the Kirsten, Harvey, and neuroblastoma oncogenes which are immunologically distinct proteins, but similar in function. The ras superfamily is usually divided into three families, ras, rab, and rho.