Within the large family of mitogen activated protein kinases (MAPKs), one outlier group referred to as atypical MAPKs is not regulated by conventional upstream MAPK kinases (MAP2Ks). This includes the Dictyostelium discoideum atypical MAPK Erk2, a protein kinase essential for chemotactic movement and development. The regulation and functional specificity of Erk2 was investigated through phenotypic analysis of chimeric and mutant MAPKs. Chimeric MAPKs containing regions of Erk2 were created using complementary regions of the more typical MAPK Erk1, that provides very different functions in this amoeba. The chimeric MAPKs were not phosphorylated at levels observed for wild-type MAPKs and none rescued wild-type MAPK function to erk1