Rap1 is a small G protein, necessary for prolonged ERK activity in PC12 cells. In such cells, NGF triggers a program of neuronal differentiation through the activation of a Rap1:B-RAF:ERK module Rap1 is activated by NGF, but not by epidermal growth factor (EGF), although both growth factors cause transient activation of RAS. Activation of Rap1 by NGF requires internalization of TRKA to intracellular vesicles, mostly endosomes, containing Rap1, B-RAF, MEK and ERKs. Rap1 does not co-localize with RAS. Therefore, the ability of Rap1 to bind RAF-1 without activating it might sequester RAF-1 from RAS. Activation of GEFs that couple to Rap1 as well as RAS might provide a mechanism to limit signals to RAS.