Identification of a dual-specificity protein phosphatase that inactivates a MAP kinase from Arabidopsis

Mitogen-activated protein kinases (MAPKs) play a key role in plant response s to stress and pathogens. Activation and inactivation of MAPKs involve pho sphorylation and dephosphorylation on both threonine and tyrosine residues in the kinase domain. Here we report the identification of an Arabidopsis g ene encoding a dual-specificity protein phosphatase capable of hydrolysing both phosphoserine/threonine and phosphotyrosine in protein substrates. Thi s enzyme, designated AtDsPTP1 (Arabidopsis thaliana dual-specificity protei n tyrosine phosphatase), dephosphorylated and inactivated AtlWPK4, a MARK m ember from the same plant. Replacement of a highly conserved cysteine by se rine abolished phosphatase activity of AtDsPTP1, indicating a conserved cat alytic mechanism of dual-specificity protein phosphatases from all eukaryot es.