| RasGEFs are now seen as signaling adaptors and integrators, they couple various signaling processes at the cell membrane to Ras and thus to changes inside the cell. The best understood signals to Ras derive from receptor tyrosine kinases (RTKs). When RTKs are stimulated by their ligands, they recruit adaptors such as Grb2, which bind directly to RasGEFs. This recruitment localizes the RasGEFs to the membrane and thus brings them into proximity with Ras. Other RasGEFs are activated by different signals, for example Ca2+ , but the underlying mechanism is thought to be similar. |