The protein encoded by the RAF1 gene is a MAP kinase kinase kinase (MAP3K) downstream of the Ras family of membrane-associated GTPases, to which it binds directly. Upon its activation, the cellular RAF1 protein can phosphorylate to activate the dual specific protein kinases MEK1 and MEK2, which in turn phosphorylate to activate the serine/threonine-specific protein kinases ERK1 and ERK2. Activated ERKs are pleiotropic effectors of cell physiology and play an important role in controlling gene expression involved in the cell division cycle, apoptosis, cell differentiation, and cell migration. Mutations in this gene are associated with Noonan syndrome 5 and LEOPARD syndrome 2.