Structure and phosphorylation of eukaryotic initiation factor 2. Casein kinase 2 and protein kinase C phosphorylate distinct but adjacent sites in the beta-subunit.
Eukaryotic initiation factor 2 (eIF-2) from rabbit reticulocytes can be phosphorylated on its beta-subunit by two different protein kinases, protein kinase C and casein kinase 2. Phosphorylation by these kinases is additive, suggesting that they phosphorylate different sites (serine residues) in eIF-2 beta. Two-dimensional peptide mapping of the phosphopeptides generated from labelled eIF-2 beta by digestion with trypsin, cyanogen bromide or Staphylococcus aureus V8 proteinase showed that protein kinase C and casein kinase 2 phosphorylated distinct and different sites in this protein. This conclusion was supported by the results of analysis of the phosphopeptides on reverse-phase chromatography. Analysis of the phosphopeptides derived from eIF-2 beta labelled by both kinases together strongly suggested that the sites labelled by protein kinase C and casein kinase 2 are adjacent in the primary sequence. These data are discussed in the light of the present understanding of the sequence specificity of the kinases. Rat liver eIF-2 beta was also found to be a substrate for protein kinase C and casein kinase 2, which were again shown to label different serine residues.
Department of Biochemistry, University of Bristol Medical School, U.K.
S J
SJ
Clark
D R
DR
Colthurst
C G
CG
Proud
D000595:Amino Acid Sequence; D000818:Animals; D047388:Casein Kinases; D020652:Peptide Elongation Factor 2; D010445:Peptide Elongation Factors / Q000378:metabolism*; D010449:Peptide Mapping; D010766:Phosphorylation; D010768:Phosphoserine / Q000096:biosynthesis; D011493:Protein Kinase C / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D011817:Rabbits; D013379:Substrate Specificity
D020652:Peptide Elongation Factor 2; D010445:Peptide Elongation Factors; D010768:Phosphoserine; D011494:Protein Kinases; D047388:Casein Kinases; D011493:Protein Kinase C