Mixed lineage kinases (MLKs) are a family of protein kinases sharing two leucine zipper-like motifs which mediate protein dimerization, and a kinase domain with a similar primary structure to both the tyrosine-specific and the serine/threonine-specific kinase classes. Members of the MLK family include MLK1, MLK2, MLK3, MLK4, MELK, LZK and DLK. MLKs are expressed in neuronal cells where they are likely to interact between Rac1/Cdc42, MKK4 and MKK7 in death signaling. Leucine zipper-bearing kinase (LZK) also activates the c-Jun-NH2 terminal kinase/stress-activated protein kinase (JNK/ SAPK) pathway though MKK7. Through its dual leucine zipper-like motif, LZK forms dimers/oligomers which are important for activation of the JNK/SAPK pathway. LZK is predominantly expressed in the pancreas, while moderate expression is observed in adult brain, liver and placenta tissues.