MLK3 (Mixed lineage kinase 3) is a serine/threonine kinase that has an amino-terminal SH3 domain followed by the kinase domain and two leucine zippers, a cdc42/Rac1 binding (CRIB) domain and several other domains/motifs at the carboxy-terminal region. MLK3 functions as a MAPKKK of the SAPK/JNK stress pathway by directly phosphorylating SEK1/MKK4 and MKK7, although it is controversial whether MLK3 is involved in p38 stress pathway activation. MLK3 also functions as an IκB kinase and mediates the activation of the transcriptional factor NF-κB stimulated by CD3/CD28, suggesting a role for MLK3 in immune and inflammatory responses.Synonyms: MLK3, Mitogen-activated protein kinase kinase kinase 11, Mixed lineage kinase 3, PTK1, Src-homology 3 domain-containing proline-rich kinase