Protein synthesis in rabbit reticulocytes: characteristics of CO-eIF-2 protein complex.
A high molecular weight reticulocyte protein factor, named Co-eIF-2, contains Co-eIF-2A, Co-eIF-2B, and Co-eIF-2C activities and stimulates Met-tRNAf binding to eIF-2 both in the presence and absence of Mg2+. Some characteristics of this stimulation in the absence of Mg2+ are: (1) Stimulation is most pronounced at low eIF-2 levels. (2) Stimulation is partially resistant to heat and NEM treatment, and thus appears to be due to the combined action of both heat and NEM-insensitive Co-eIF-2A, and heat and NEM-sensitive Co-eIF-2C activities. (3) [3H]GDP bound in eIF-2 . [3H]GDP complex is rapidly displaced by unlabelled GTP during ternary complex formation Co-eIF-2 stimulates Met-tRNAf binding to eIF-2 even when added after the [3H]GDP from eIF-2 . [3H]GDP has been completely displaced. This indicates that Co-eIF-2-stimulation is not due to GDP displacement from eIF-2 . GDP. We propose that eIF-2 molecules become inactive in the presence of Mg2+ and at high dilution, and Co-eIF-2 restores the inactive eIF-2 molecules into an active form.
D000818:Animals; D015852:Eukaryotic Initiation Factor-2; D020662:Guanine Nucleotide Exchange Factors; D007700:Kinetics; D046911:Macromolecular Substances; D010448:Peptide Initiation Factors / Q000235:genetics*; D011485:Protein Binding; D014176:Protein Biosynthesis; D011506:Proteins / Q000235:genetics*; D012346:RNA, Transfer, Amino Acyl / Q000235:genetics; D012358:RNA, Transfer, Met; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism*
D015852:Eukaryotic Initiation Factor-2; D020662:Guanine Nucleotide Exchange Factors; D046911:Macromolecular Substances; D010448:Peptide Initiation Factors; D011506:Proteins; D012346:RNA, Transfer, Amino Acyl; D012358:RNA, Transfer, Met; C024988:tRNA, formylmethionine-