- Targeted disruption of the MKK4 gene causes embryonic death, inhibition of c-Jun NH2-terminal kinase activation, and defects in AP-1 transcriptional activity. Yang, D., Tournier, C., Wysk, M., Lu, H.T., Xu, J., Davis, R.J., Flavell, R.A. Proc. Natl. Acad. Sci. U.S.A. (1997)