Catalytic domain of the Serine/Threonine Kinase, c-Jun N-terminal Kinase 1STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. JNK1 is expressed in every cell and tissue type. It specifically binds with JAMP (JNK1-associated membrane protein), which regulates the duration of JNK1 activity in response to stimuli. Specific JNK1 substrates include Itch and SG10, which are implicated in Th2 responses and airway inflammation, and microtubule dynamics and axodendritic length, respectively. Mice deficient in JNK1 are protected against arthritis, obesity, type 2 diabetes, cardiac cell death, and non-alcoholic liver disease, suggesting that JNK1 may play roles in the pathogenesis of these diseases. Initially, it was thought that JNK1 and JNK2 were functionally redundant as mice deficient in either genes could survive but disruption of both genes resulted in lethality. However, recent studies have shown that JNK1 and JNK2 perform distinct functions through specific binding partners and substrates. JNKs are mitogen-activated protein kinases that are involved in many stress-activated responses including those during inflammation, neurodegeneration, apoptosis, and persistent pain sensitization, among others. The JNK1 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.