Phosphorylation of maize RAB-17 protein by casein kinase 2.
The maize gene RAB-17, which is responsive to abscisic acid, encodes a basic glycine-rich protein containing, in the middle part of its sequence, a cluster of 8 serine residues followed by a putative casein kinase 2-type substrate consensus sequence. This protein was found to be highly phosphorylated in vivo. Here, we show that RAB-17 protein is a real substrate for casein kinase 2. RAB-17 protein is phosphorylated in vitro by casein kinase 2 isolated from rat liver cytosol and from maize embryos. A maximum of 4 mol of phosphate were incorporated per mol of RAB-17 protein following incubation with casein kinase 2. Phosphopeptide mapping experiments show that the peptide phosphorylated by casein kinase 2 in vitro is identical to that derived from the protein phosphorylated in vivo. Purification by high performance liquid chromatography and partial sequencing of the phosphopeptide indicate that it corresponds to the region of the protein (residues 56-89) containing the cluster of serine residues. Our results indicate that RAB-17 is phosphorylated by casein kinase 2 or a kinase with a similar specificity and that phosphorylation takes place in the serine cluster region of the protein both in vitro and in vivo.
Departament de Genética Molecular, Centre d'Investigació i Desenvolupament, Barcelona, Spain.
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Plana
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Itarte
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Eritja
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Goday
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Pagès
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Martínez
D000595:Amino Acid Sequence; D000818:Animals; D047388:Casein Kinases; D002851:Chromatography, High Pressure Liquid; D002852:Chromatography, Ion Exchange; D003600:Cytosol / Q000201:enzymology; D004591:Electrophoresis, Polyacrylamide Gel; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010449:Peptide Mapping; D010748:Phosphopeptides / Q000302:isolation & purification; D010766:Phosphorylation; D010940:Plant Proteins / Q000302:isolation & purification / Q000378:metabolism*; D011494:Protein Kinases / Q000302:isolation & purification / Q000378:metabolism*; D051381:Rats; D012639:Seeds / Q000201:enzymology; D003313:Zea mays / Q000201:enzymology / Q000378:metabolism*
D010748:Phosphopeptides; D010940:Plant Proteins; C071710:DHN1 protein, Zea mays; D011494:Protein Kinases; D047388:Casein Kinases