Relative expression levels of MAP kinases and MAP kinase kinases in diverse tissues and organs. Western blotting was used to quantify the relative protein levels of (a) ERK1 and ERK2 and (b) MEK1 and MEK2 in 306 human (Hu) and mouse (Mo) tissue and organ specimens. Values are the mean of at least triplicate (range 3 to 38) determinations from measurements for each kinase in 33 diverse tissues and organs analyzed by Kinetworks™ Protein Kinase Screen (KPKS) immunoblotting . The mean values for kinase expression from the pooled average values from 30 different cultured tumor cell lines evaluated with another 111 Kinetworks™ KPKS immunoblots are also shown at the top of each panel. Equivalent total amounts of proteins from tissue or cell lysates were assayed on each immunoblot, and the relative affinities for the antibodies for their target proteins were comparable.