Figure 1.

The two states of RAS family GTPases. GTP- and GDP-bound states are directed by GEFs and GAPs. GEFs stimulate the exchange of GDP to GTP, promoting activation of RAS (On). GAPs drive GTP hydrolysis and return to inactive GDP-bound status (Off). The thickness of the arrows indicates the strength of GTP binding as well as the (hyper)activation of downstream effectors. The red cross indicates the impairment of GTP hydrolysis. GEF: guanine nucleotide exchange factor; GAP: GTPase-activating protein; GTP: guanosine triphosphate; GDP: guanosine diphosphate; RAS: rat sarcoma proto-oncogene