Protein synthesis in rabbit reticulocytes XXII: A heat stable dialyzable factor (EIF-1∗) modulates Met-tRNAf binding to EIF-1

Abstract

The peptide chain initiation factor EIF-1 forms a ternary complex, Met-tRNAf·EIF-1·GTP in the absence of Mg++ and the preformed complex is stable to Mg++. However, with homogeneous preparations of EIF-1, addition of Mg++ during the initial formation of the ternary complex strongly inhibits the complex formation.A heat stable dialyzable factor (EIF-1∗) which mostly remains associated with the high molecular weight protein complex, EIF-2 (TDF) during purification of the peptide chain initiation factors, has been purified using a phenol extraction procedure. EIF-1∗ restores the Met-tRNAf binding activity of EIF-1 in the presence of 1 mM Mg++; in the presence of EIF-1∗, Met-tRNAf binding by EIF-1 shows a sharp Mg++ optimum around 1 mM. EIF-1∗ is heat stable, alkali stable, dialyzable and pronase sensitive. The same EIF-1∗ preparation also strongly inhibits Met-tRNAf binding to EIF-1 in the absence of Mg++ and stimulates protein synthesis in a mRNA-dependent rabbit reticulocyte lysate system.