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Catalytic domain of the Serine/Threonine Kinase, c-Jun N-terminal Kinase STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. JNKs are mitogen-activated protein kinases (MAPKs) that are involved in many stress-activated responses including those during inflammation, neurodegeneration, apoptosis, and persistent pain sensitization, among others. They are also essential regulators of physiological and pathological processes and are involved in the pathogenesis of several diseases such as diabetes, atherosclerosis, stroke, Parkinson's and Alzheimer's. Vetebrates harbor three different JNK genes (Jnk1, Jnk2, and Jnk3) that are alternatively spliced to produce at least 10 isoforms. JNKs are specifically activated by the MAPK kinases MKK4 and MKK7, which are in turn activated by upstream MAPK kinase kinases as a result of different stimuli including stresses such as ultraviolet (UV) irradiation, hyperosmolarity, heat shock, or cytokines. JNKs activate a large number of different substrates based on specific stimulus, cell type, and cellular condition, and may be implicated in seemingly contradictory functions. The JNK subfamily is part of a larger superfamily that includes the catalytic domains of other STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase.
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