Phosphorylation of the C2 subunit of the proteasome in rice (Oryza sativa L.).
Proteasomes function mainly in the ATP-dependent degradation of proteins that have been conjugated with ubiquitin. To demonstrate the phosphorylation of proteasomes in plants, we conducted an enzymatic dephosphorylation experiment with a crude extract of rice cultured cells. The results indicated that the C2 subunit of the 20S proteasome is phosphorylated in vivo in cultured cells. An in-gel kinase assay and analysis of phospho-amino acids revealed that the C2 subunit is phosphorylated by a 40-kDa serine/threonine protein kinase, the activity of which is inhibited by heparin, a specific inhibitor of casein kinase II. The catalytic subunit of casein kinase II from Arabidopsis was also able to phosphorylate the C2 subunit. These results suggest that the C2 subunit in rice is probably phosphorylated by casein kinase II. Our demonstration of the phosphorylation of proteasomes in plants suggests that phosphorylation might be involved in the general regulation of the functions of proteasomes.
Umeda
M
M
Institute of Molecular and Cellular Biosciences, University of Tokyo, Japan.
Manabe
Y
Y
Uchimiya
H
H
D017360:Arabidopsis / Q000201:enzymology; D047390:Casein Kinase II; D002478:Cells, Cultured; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006493:Heparin / Q000494:pharmacology; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009097:Multienzyme Complexes / Q000378:metabolism*; D012275:Oryza / Q000201:enzymology*; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins
D004791:Enzyme Inhibitors; D009097:Multienzyme Complexes; D011993:Recombinant Fusion Proteins; D006493:Heparin; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex