Figure 5.

Signaling pathways downstream of Ras, a farnesylated small GTPase. Ras directly activates the mitogen activated protein kinase (MAPK) cascade, through phosphorylation of Raf (or other MAPK kinase kinase, MAPKKK) which in turn phosphorylates MEK (or other MAPK kinases), which then phosphorylates MAPK. On the other hand, Ras also activates Rac GTPases, which in turn activates p21-activated kinase (PAK), an Akt interacting protein. Rac also can activate Rho GTPases, which regulates actin stress fiber and focal adhesion formation by activating Rho kinase, which in turn regulates the activity of myosin light chain which controls actin polymerization.