 There have been no functional differences documented between the 46 kDa and the 55 kDa isoform, however, a second form of alternative splicing occurs within transcripts of JNK1 and JNK2, yielding JNK1-α, JNK2-α and JNK1-β and JNK2-β.Differences in interactions with protein substrates arise because of the mutually exclusive utilization of two exons within the kinase domain.c-Jun N-terminal kinase isoforms have the following tissue distribution