MAP kinase pathways consist of three kinases, shown here are Raf kinase (MAPKKK, MAPKK kinase; phosphorylates MAPKK), MEK (MAPK/ERK kinase, MAPKK; the kinase of MAPK), and ERK (extracellular signal-regulated kinase, MAPK, MAP kinase). Phosphorylation activates the next kinase in the cascade. Information is transduced from Raf to ERK, and negative feedback regulation occurs through phosphorylation of Raf by ERK in minutes to switch off signalling. In addition to phosphorylating Raf, active ERK translocates to the cell nucleus to activate gene transcription. * indicates the active enzyme.