MAPK (Mitogen-Activated Protein Kinase) signal transduction pathways are evolutionarily conserved in eukaryotic cells and transduce signals in response to a variety of extracellular stimuli. Each pathway is composed of three classes of protein kinase: MAPK, MAPKK (MAPK Kinase) and MAPKKK (MAPK Kinase Kinase). MAPK is activated by tyrosine and threonine phosphorylation catalyzed by a family of dual-specificity protein kinase MAPKKs. MAPKK is in turn activated by phosphorylation mediated by MAPKKK. Cascades of MAPKs mediate responses such as cell proliferation, differentiation, and the regulation of metabolic pathways. There are multiple MAPKs in eukaryotes. Three subgroups of the MAPK superfamily have been identified in mammals: ERK (Extracellular signal-Regulated Kinase), JNK (c-Jun N-terminal Kinase) and p38 (or Mpk2). Drosophila melanogaster expresses all three [...]