JAK2, a member of the Janus kinase super- family was found to interact functionally with Raf-1, a central component of the ras/mitogen-activated protein kinase signal transduction pathway. Interferon-γ and several other cyto- kines that are known to activate JAK2 kinase were also found to stimulate Raf-1 kinase activity toward MEK-1 in mamma- lian cells. In the baculovirus coexpression system, Raf-1 was activated by JAK2 in the presence of p21~ras. Under these conditions, a ternary complex of p21~ras, JAK2, and Raf-1 was observed. of the United States of America
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