Protein synthesis in rabbit reticulocytes XXI. Purification and properties of a protein factor (Co-EIF-1) which stimulates Met-tRNAf binding to EIF-1.
The peptide chain initiation factor, Co-EIF-1 has been purified to homogeneity. Upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the homogeneous preparation gives a single protein band corresponding to a molecular weight of approximately 20,000. In the crude preparation, Co-EIF-1 exists in two molecular forms: Co-EIF-1H (Mr = 200,000) and Co-EIF-1L (Mr = 20,000). Both forms are equally active in all the reactions studied. Upon heating, the heavy form (Co-EIF-1H) is completely converted into the light form (Co-EIF-1L). Radioactively labeled [14C]Co-EIF-1 was prepared by reductive alkylation using [14C]formaldehyde and borohydride. [14C]Methyl-Co-EIF-1 binds specifically to EIF-1; EIF-1.[14C]Co-EIF-1 complex was analyzed by gel (Sephadex G-100) filtration. EIF-1.Co-EIF-1 complex is distinctly more stable towards heat than EIF-1 alone and the quarternary complex, Met-tRNAf.EIF-1.Co-EIF-1.GTP is more resistant to aurintricarboxylic acid than the ternary complex, Met-tRNAf.EIF-1.GTP. Both the quarternary complex, Met-tRNAf.EIF-1.Co-EIF-1.GTP, and the ternary complex, Met-tRNAf.EIF-1.GTP, are equally sensitive to Mg2+ in the presence of EIF-2 (TDF). In the presence of Co-EIF-1, the initial rate of Met-tRNAf binding to 40 S ribosomes was significantly increased.
D000818:Animals; D006150:Guanine Nucleotides / Q000378:metabolism; D007700:Kinetics; D008715:Methionine; D010442:Peptide Chain Initiation, Translational; D010448:Peptide Initiation Factors; D011485:Protein Binding; D011506:Proteins / Q000302:isolation & purification / Q000378:metabolism*; D012346:RNA, Transfer, Amino Acyl / Q000097:blood*; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism*
D006150:Guanine Nucleotides; D010448:Peptide Initiation Factors; D011506:Proteins; D012346:RNA, Transfer, Amino Acyl; D008715:Methionine