Release of IF2 from native ribosomes by dilution

In E. coli, IF2 and other polypeptide chain initiation factors have been shown to be associated with the native 30s ribosomal subunits [ 1, 21. These factors are removed by washing the ribosomes with a buffer containing relatively high (0.5-1.0 M) concentrations of NH&l. However, in certain eukaryotic systems, e.g., Artemia salina embryos [3], rat liver [4], wheat germ [5], initiation factors, functionally similar to IF2, are found in the postribosomal supernatant even though the subcellular fractions are prepared in a buffer containing a relatively low concentration of monovalent cation. In the reticulocyte system under these conditions, there is evidence that the initiation factors are ribosome-associated [6] as well as free in the cytoplasm [7]. The present study shows that much of the IF2 is released when native ribosomes are simply diluted in a buffer containing relatively low (0.05 M) concentration of NH&l. These results are consistent with the idea [8] that, as in the case of IF3 [9], the interaction of IF2 with the 30s subunit may involve the equilibrium: IF2 + 30s * [IF2-30S].