MEK1 is an activator and kinase for MAP and ERK kinases. It is a serine/threonine kinase essential to the MAP kinase signal transduction pathway which is involved in a multitude of cellular processes such as proliferation, differentiation, gene activation, and development. MEK1 displays 85% identity with MEK2. Although MEK1 and MEK2 have been found to be functionally similar, they may serve non-redundant functions. Both are required for cellular proliferation and may play a role in tumorigenesis.