title: Xenopus MAP kinase activator: identification and function as a key intermediate in the phosphorylation cascade.
abstract: MAP kinase is thought to play a pivotal role not only in the growth factor-stimulated signalling pathway but also in the M phase phosphorylation cascade downstream of MPF. MAP kinase is fully active only when both tyrosine and threonine/serine residues are phosphorylated. We have now identified and purified a Xenopus MAP kinase activator from mature oocytes that is able to induce activation and phosphorylation on tyrosine and threonine/serine residues of an inactive form of Xenopus MAP kinase. The Xenopus MAP kinase activator itself is a 45 kDa phosphoprotein and is inactivated by protein phosphatase 2A treatment in vitro. Microinjection of the purified activator into immature oocytes results in immediate activation of MAP kinase. Further experiments using microinjection as well as cell free extracts have shown that Xenopus MAP kinase activator is an intermediate between MPF and MAP kinase. Thus, MAP kinase activator plays a key role in the phosphorylation cascade.
authors.affiliation: Department of Biophysics and Biochemistry, Faculty of Science, University of Tokyo, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Matsuda
authors.forename: H
authors.initials: H
authors.lastname: Kosako
authors.forename: K
authors.initials: K
authors.lastname: Takenaka
authors.forename: K
authors.initials: K
authors.lastname: Moriyama
authors.forename: H
authors.initials: H
authors.lastname: Sakai
authors.forename: T
authors.initials: T
authors.lastname: Akiyama
authors.forename: Y
authors.initials: Y
authors.lastname: Gotoh
authors.forename: E
authors.initials: E
authors.lastname: Nishida
mesh_terms: D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002474:Cell-Free System; D002848:Chromatography, DEAE-Cellulose; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D008845:Microinjections; D008969:Molecular Sequence Data; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010750:Phosphoproteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D054648:Protein Phosphatase 2; D015398:Signal Transduction; D014981:Xenopus
chemical_list: D010750:Phosphoproteins; D011494:Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2