Monomeric, autoinhibited basal state. The most important MAP3K substrates within the JNK pathway are the MAP2Ks known as MKK4 and MKK7 (Fig. 1). MAP2Ks are highly specialized proteins of the STE kinase family, and MAP3K-mediated phosphorylation is the only reported activation mechanism for MKK4 or MKK7 under physiological conditions. Most MAP3Ks involved in the JNK pathway can phosphorylate multip