phosphorylated at the Thr-Pro-Tyr phosphorylation motif instead of the characteristic MAP kinase Thr-Glu-Tyr motif. JNK2 (p54a, SAPK1a), along with JNK1 and JNK3, is thought to play an important role in nuclear signal transduction through its environmental stress activation and subsequent phosphorylation of the nuclear transcription factor p53.