Zapata J M, Martínez M A, Sierra J M
Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas, Madrid, Spain.
J Biol Chem. 1994 Jul 8;269(27):18047-52.
The eukaryotic polypeptide chain initiation factor 4F (eIF-4F), purified by m7GTP-Sepharose chromatography from whole extracts of Drosophila melanogaster embryos, consists of two subunits, the previously identified eIF-4E (35 kDa) (Maroto, F. G., and Sierra, J. M. (1989) Mol. Cell. Biol. 9, 2181-2190) and another of 200 kDa. Both subunits cosedimented through a sucrose density gradient containing 0.5 M KCl. In contrast to rabbit reticulocyte eIF-4F, we did not find any RNA-dependent ATPase associated with the Drosophila factor. As shown previously for eIF-4E, the p200 subunit was also required for the translation of endogenous mRNAs in cell-free systems from Drosophila embryos. Only the eIF-4E subunit was able to cross-link to the m7G cap structure. However, an efficient cross-linking of the p200 subunit to an uncapped mRNA was observed. Both subunits were phosphorylated in vitro by protein kinase C from rat brain. As an extension of our previous results (Zapata, J. M., Maroto, F. G., and Sierra, J. M. (1991) J. Biol. Chem. 266, 16007-16014) we found that the translation of the heat shock mRNAs was independent of both of the eIF-4F subunits.
通过m7GTP - 琼脂糖凝胶层析从黑腹果蝇胚胎的全提取物中纯化得到的真核多肽链起始因子4F（eIF - 4F）由两个亚基组成，一个是先前鉴定出的eIF - 4E（35 kDa）（马罗托，F.G.，和西拉，J.M.（1989年）《分子与细胞生物学》9，2181 - 2190），另一个是200 kDa的亚基。两个亚基在含有0.5 M KCl的蔗糖密度梯度中共同沉降。与兔网织红细胞eIF - 4F不同，我们未发现与果蝇因子相关的任何RNA依赖性ATP酶。如先前对eIF - 4E的研究所示，在来自果蝇胚胎的无细胞系统中，内源性mRNA的翻译也需要p200亚基。只有eIF - 4E亚基能够与m7G帽结构交联。然而，观察到p200亚基与无帽mRNA的有效交联。两个亚基在体外都被大鼠脑的蛋白激酶C磷酸化。作为我们先前研究结果（萨帕塔，J.M.，马罗托，F.G.，和西拉，J.M.（1991年）《生物化学杂志》266，16007 - 16014）的延伸，我们发现热休克mRNA的翻译与eIF - 4F的两个亚基均无关。
