Enables MAP kinase kinase activity. Acts upstream of or within several processes, including ERK1 and ERK2 cascade; animal organ development; and neurogenesis. Predicted to be located in several cellular components, including dendrite cytoplasm; perikaryon; and perinuclear region of cytoplasm. Predicted to colocalize with microtubule. Is expressed in several structures, including alimentary system; early conceptus; genitourinary system; nervous system; and sensory organ. Used to study cardiofaciocutaneous syndrome. Human ortholog(s) of this gene implicated in carcinoma (multiple); cardiofaciocutaneous syndrome 3; high grade glioma; and melorheostosis. Orthologous to human MAP2K1 (mitogen-activated protein kinase kinase 1). [provided by Alliance of Genome Resources, Apr 2022]