MEK1 (MAP2K1)

MEK1, encoded by MAP2K1, is the dual-specificity kinase in the middle of the MAPK cascade that phosphorylates ERK in response to RAS-pathway signals.

Function

MEK1 sits between the RAF kinases and ERK. Activated BRAF phosphorylates MEK1 on two serines; MEK1 then phosphorylates ERK1/2 on both a threonine and a tyrosine - the dual specificity that gives the family its name. ERK carries the signal into the nucleus, where it phosphorylates transcription factors and drives the proliferative program. The cascade’s three-tiered structure (RAS → RAF → MEK → ERK) amplifies the signal at each step, and feedback phosphorylation from ERK back onto upstream components