A family of protein kinases located upstream of the MAP kinases and responsible for their activation has been identified. This kinase specifically interacts with and activates MAPK7/ERK5. MEK-3 (or MKK-3) functions to activate p38 MAP kinase, and MEK-4 (also called SEK1 or MKK-4) activates both p38 and JNK MAP kinases.
