MEK2 IS A KINASE RELATED TO MEK1 AND TS DIFFERENTIALLY EXPRESSED IN MURINE TISSUES

MEK1 is a dual specificity kinase that phosphorylates and activates the Erk/MAP kinases Erk-1 and Erk-2 by phosphorylating them on threonine and tyrosine. We report the cloning of a second MEK-like complementary DNA, Mek2, which predicts a protein of a molecular weight of 44,500. The MEK2 protein bears substantial sequence homology to MEK1, except at its amino terminus, and at a proline-rich region insert between the conserved kinase subdomains 9 and 10. MEK1 and MEK2 are shown to be encoded by different genes and are located on murine chromosomes 9 and 10, respectively. Northern analysis indicates that Mek2 is expressed at low levels in adult mouse brain and heart tissue, and at higher levels in other tissues examined. Low expression levels of Mek2 in brain tissue are in contrast to the high levels of Mek1 expressed in brain. Mek2 is expressed at high levels in neonatal brain, however. Recombinant MEK2 produced in bacteria phosphorylates a kinase-inactive Erk-1 on tyrosine and threonine, whereas a kinase-inactive mutant MEK2 does not. These findings suggest that MEK2 is a member of a multigene family.