title: Molecular mechanisms of control of protein biosynthesis.
abstract: Reticulocytes contain two protein kinases which, when activated, phosphorylate the alpha subunit of the chain initiation factor eIF-2 interfering with its function. One kinase is activated in the absence of heme, the other is activated by low concentrations of double-stranded RNA. Both appear to be active in a phosphorylated form. Phosphorylation of the eIF-2 alpha subunit does not modify the basic properties of the factor but prevents its interaction with a stimulating protein (SP) required for binary complex formation at low, physiological concentrations of eIF-2 and Mg 2+. SP, isolated in the form of an eIF-2 complex (eIF-2. SP) of high molecular weight (approximately 450000), promotes formation of a GTP . eIF-2 binary complex, the first step of initiation, in a catalytic fashion. The available evidence suggests that eIF-2 . SP can form in the presence of Mg 2+ a GTP . eIF-2 . SP complex that interacts with free eIF-2 forming GTP . eIF-2 (binary complex) and eIF-2. SP.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D015852:Eukaryotic Initiation Factor-2; D005914:Globins / Q000096:biosynthesis; D020662:Guanine Nucleotide Exchange Factors; D006160:Guanosine Triphosphate / Q000378:metabolism; D008274:Magnesium / Q000494:pharmacology; D010442:Peptide Chain Initiation, Translational; D010448:Peptide Initiation Factors / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D011506:Proteins / Q000302:isolation & purification / Q000378:metabolism* / Q000502:physiology*; D012346:RNA, Transfer, Amino Acyl / Q000378:metabolism; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism
chemical_list: D015852:Eukaryotic Initiation Factor-2; D020662:Guanine Nucleotide Exchange Factors; D010448:Peptide Initiation Factors; D011506:Proteins; D012346:RNA, Transfer, Amino Acyl; C026464:tRNA(m)(Met), methionine-; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D005914:Globins; D011494:Protein Kinases; D008274:Magnesium