Mehta H B, Woodley C L, Wahba A J
J Biol Chem. 1983 Mar 25;258(6):3438-41.
We have prepared eukaryotic initiation factor 2 (eIF-2) from rabbit reticulocytes and Artemia embryos and studied the effect of Mg2+ on binary (eIF-2 X GDP) and ternary (eIF-2 X GTP X Met-tRNAf) complex formation. Under conditions where Mg2+ inhibits Met-tRNAf binding to reticulocyte eIF-2, ternary complex formation with Artemia eIF-2 is not inhibited. Similarly, the formation of eIF-2 X GDP with Artemia eIF-2 is stimulated by Mg2+, whereas the corresponding reticulocyte binary complex is strongly inhibited. In the presence of 1 mM Mg2+, the isolated Artemia eIF-2 X GDP complex is stable in the absence of any added nucleotide, but readily exchanges bound GDP for free GTP. However, the reticulocyte eIF-2 X GDP complex is significantly more stable in the presence of GTP, and nucleotide exchange is dependent upon the addition of a factor isolated from either the postribosomal supernatant or the high salt wash of rabbit reticulocyte ribosomes. This factor also stimulates Met-tRNAf binding to both Artemia and reticulocyte eIF-2.
我们从兔网织红细胞和卤虫胚胎中制备了真核起始因子2（eIF - 2），并研究了Mg2 +对二元复合物（eIF - 2·GDP）和三元复合物（eIF - 2·GTP·Met - tRNAf）形成的影响。在Mg2 +抑制Met - tRNAf与网织红细胞eIF - 2结合的条件下，卤虫eIF - 2形成三元复合物并未受到抑制。同样，Mg2 +刺激卤虫eIF - 2形成eIF - 2·GDP，而相应的网织红细胞二元复合物则受到强烈抑制。在1 mM Mg2 +存在下，分离得到的卤虫eIF - 2·GDP复合物在未添加任何核苷酸时是稳定的，但能轻易地将结合的GDP与游离GTP进行交换。然而，网织红细胞eIF - 2·GDP复合物在GTP存在时稳定性显著更高，并且核苷酸交换依赖于添加从兔网织红细胞核糖体的核糖体后上清液或高盐洗涤液中分离得到的一种因子。该因子也刺激Met - tRNAf与卤虫和网织红细胞的eIF - 2结合。
