c-Jun N-terminal kinase (JNK) is one of the several main MAP kinase groups identified in mammals. Recent evidences suggest that activation of JNK may play an important role in neuronal apoptosis and other physiological and pathological processes. The JNK Activity screening kit utilizes an N-terminal c-Jun (1-79) fusion protein bound to glutathion sepharose beads to selectively “pull down” JNK from cell lysates. After wash to remove nonspecifically bound proteins, the kinase reaction is then carried out in the presence of cold ATP. c-Jun phosphorylation is then measured by Western blot analysis using a phospho-c-Jun specific antibody.