An isolated polypeptide (JNK) characterized by having a molecular weight of 46 kD as determined by reducing SDS-PAGE, having serine and threonine kinase activity, phosphorylating the c-Jun N-terminal activation domain and polynucleotide sequences and method of detection of JNK are provided herein. JNK phosphorylates c-Jun N-terminal activation domain which affects gene expression from AP-1 sites.
 This invention was made with support by Howard Hughes Medical Institute and Government support under Grant No. DE-86ER60429, awarded by the Department of Energy and Grant No. CA-50528 and CA-58396, awarded by the National Institute of Health. The Government has certain rights in this invention. Also supported by the Howard Hughes Medical Institute.