Phosphorylation of Xenopus mitogen-activated protein (MAP) kinase kinase by MAP kinase kinase kinase and MAP kinase.
Xenopus 45-kDa mitogen-activated protein (MAP) kinase kinase (MAPKK) is a serine/threonine/tyrosine kinase, which activates MAP kinase (MAPK) by phosphorylating its threonine and tyrosine residues. MAPKK is active only when its threonine and/or serine residues are phosphorylated. We have identified from Xenopus eggs two protein kinases responsible for phosphorylation of MAPKK. The two kinases are separated by Sephacryl S-300 gel filtration chromatography. The higher molecular weight kinase phosphorylates MAPKK previously dephosphorylated and inactivated by phosphatase 2A treatment on mainly serine and slightly threonine residues, and reactivates the MAPKK, and is thus assumed to work as MAPKK kinase (MAPKKK) in vivo. The lower molecular weight kinase, identified as MAPK, phosphorylates the dephosphorylated MAPKK on mainly threonine and faintly serine residues, but does not reactivate the MAPKK activity. As Xenopus MAPKK contains a single phosphorylation consensus sequence (PXT388P) for MAPK in the C-terminal region, this T388 residue may be a major phosphorylation site catalyzed by MAPK. Thus, Xenopus MAPKK is phosphorylated in mature oocytes by not only an upstream kinase, MAPKKK, but also a downstream kinase, MAPK.
Department of Biophysics and Biochemistry, Faculty of Science, University of Tokyo, Japan.
S
S
Matsuda
Y
Y
Gotoh
E
E
Nishida
D000595:Amino Acid Sequence; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002499:Centrifugation, Density Gradient; D002850:Chromatography, Gel; D005260:Female; D020930:MAP Kinase Kinase Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000201:enzymology*; D010766:Phosphorylation; D011494:Protein Kinases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D014981:Xenopus
D011994:Recombinant Proteins; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D020930:MAP Kinase Kinase Kinases; D020929:Mitogen-Activated Protein Kinase Kinases