Partial purification and characterization of a 90,000-dalton peptide involved in activation of the eIF-2 alpha protein kinase of the hemin-controlled translational repressor.
In the absence of heme, a negative translational control system is activated in reticulocytes or their lysates that causes the phosphorylation of the smallest subunit of peptide initiation factor 2 and the inhibition of peptide initiation. Two partially purified enzyme fractions are shown to give a concerted effect for phosphorylation of this subunit of initiation factor 2 and binding of methionyl-tRNAf to 40S ribosomal subunits. One enzyme fraction contains a 90,000-dalton peptide that functions in activation of an enzyme containing a 100,000-dalton peptide of the other fraction. Phosphorylation of the 100,000-dalton peptide is correlated with activation of the kinase for the smallest subunit of initiation factor 2. Antibodies against the 90,000-dalton peptide decrease phosphorylation of both the 100,000-dalton peptide and the subunit of initiation factor 2. The results indicate that at least two components function in a sequence of reactions that inhibits protein synthesis by phosphorylation of the smallest subunit of eucaryotic initiation factor 2. The same sequence may be activated in the presence of heme by a cascade type of reactions initiated by a heat-stable protein, HS [Henderson, A.B., Miller, A.H., & Hardesty, B. (1979) Proc. Natl. Acad. Sci. U.S.A. 76, 2605-2609].
D000818:Animals; D001798:Blood Proteins / Q000302:isolation & purification / Q000502:physiology*; D003429:Cross Reactions; D015852:Eukaryotic Initiation Factor-2; D006418:Heme / Q000494:pharmacology*; D006801:Humans; D007118:Immunoassay; D007074:Immunoglobulin G; D007700:Kinetics; D008715:Methionine; D008970:Molecular Weight; D010448:Peptide Initiation Factors / Q000378:metabolism; D014176:Protein Biosynthesis / Q000187:drug effects; D011494:Protein Kinases / Q000097:blood*; D011506:Proteins / Q000378:metabolism*; D012343:RNA, Transfer / Q000378:metabolism; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism
D001798:Blood Proteins; D015852:Eukaryotic Initiation Factor-2; D007074:Immunoglobulin G; D010448:Peptide Initiation Factors; D011506:Proteins; D006418:Heme; D012343:RNA, Transfer; D008715:Methionine; D011494:Protein Kinases