Mitogen-activated protein kinase or MAPK pathways relay signals downstream of RTKs to activate transcription factors. In the Ras-MAPK signaling pathway, Raf, the initial kinase of this pathway, binds the 14-3-3 protein dimer and remains inactive in the cytosol. Mitogen binding on the RTKs activates Ras GTP, which then binds the Raf/14-3-3 complex. Phosphorylation of multiple sites on Raf disassembles the complex allowing Raf to dimerize with a nearby phosphorylated monomer. The dimeric Raf now phosphorylates and activates another kinase, MEK , which in turn phosphorylates the cascade's final kinase, ERK. The activated ERK is transported to the nucleus to phosphorylate transcription factors such as c-Jun and c-Fos and initiate cellular processes such as cell proliferation, survival, differentiation, or apoptosis.