Details:
An intracellular protein kinase cascade containing at least ERK1 or ERK2 (MAPKs), a MEK (a MAPKK) and a MAP3K. The cascade can also contain two additional tiers: the upstream MAP4K and the downstream MAP Kinase-activated kinase (MAPKAPK). The kinases in each tier phosphorylate and activate the kinases in the downstream tier to transmit a signal within a cell. [GOC:add, GOC:signaling, ISBN:0121245462, ISBN:0896039986, PMID:20811974]