The protein encoded by this gene is a member of the serine/threonine kinase family. This kinase contains a SH3 domain and a leucine zipper-basic motif. This kinase preferentially activates MAPK8/JNK kinase, and functions as a positive regulator of JNK signaling pathway. This kinase can directly phosphorylate, and activates IkappaB kinase alpha and beta, and is found to be involved in the transcription activity of NF-kappaB mediated by Rho family GTPases and CDC42.