The mitogen-activated protein kinases (MAPK) consist of several subgroups, including the ERK, JNK, and p38 kinases. The members of this MAPK family are regulated by many different extracellular cues ranging from cytokines, growth factors, and neuropeptides (1). These stimuli activate cell surface receptors to stresses such as cold, heat, osmolarity changes and irradiation. The pathways regulated by the MAPKs control a broad array of cellular responses ranging from survival, cell proliferation, and apoptosis (1,2). The MAPKs family is also characterized by their requirement for dual phosphorylation at a conserved threonine and tyrosine residue for enzymatic activation and both must be phosphorylated for full enzymatic activation (3). The closely related ERK1 (44 kDa) and ERK2 (42 kDa) kinases are characterized by their requirement for dual phosphorylation at a conserved T-E-Y motif (4,5). While JNK1 is activated by dual phosphorylation at a T-P-Y motif and p38 is also activated by dual phosphorylation at a T-G-Y motif (6,7).