Browning K S, Humphreys J, Hobbs W, Smith G B, Ravel J M
Clayton Foundation Biochemical Institute, University of Texas, Austin 78712.
J Biol Chem. 1990 Oct 15;265(29):17967-73.
Previous work by Browning et al. (Browning, K. S., Lax, S. R., Humphreys, J., Ravel, J. M., Jobling, S. A., and Gehrke, L. (1988) J. Biol. Chem. 263, 9630-9634) indicated that wheat germ extracts do not contain sufficient amounts of some of the protein synthesis initiation factors to obtain optimal translation of all mRNAs. In this investigation, a quantitative enzyme-linked immunosorbent assay was used to determine the amounts of eukaryotic initiation factors (eIF) 2, 3, 4A, 4F, and (iso)4F as well as the amounts of 40 S ribosomal subunits and elongation factors (EF) 1 alpha and 2 present in wheat germ extracts. EF-1 alpha is present in the highest amount (approximately 5% of the total protein), and eIF-4F is present in the lowest amount (approximately 0.03% of the total protein). The micromolar amounts of the factors and ribosomes are as follows: EF-1 alpha, 34; EF-2, 5.2; eIF-2, 1.5; eIF-3, 0.7; eIF-4A, 3.0, eIF-4F, 0.09; eIF-(iso)4F, 0.8; and 40 S ribosomal subunits, 3.2. The molar ratios of the factors to 40 S ribosomal subunits are approximately 11:1 for EF-1 alpha, 1.6:1 for EF-2, 0.45:1 for eIF-2, 0.2:1 for eIF-3, 0.9:1 for eIF-4A, 0.03:1 for eIF-4F, and 0.25:1 for eIF-(iso)4F. These findings strongly suggest that the concentrations of the initiation factors, particularly those factors required for the binding of mRNA to ribosomes, may play a major role in regulating the translation of mRNAs within the cell.
布朗宁等人之前的研究工作（布朗宁，K.S.，拉克斯，S.R.，汉弗莱斯，J.，拉韦尔，J.M.，乔布林，S.A.，和盖尔克，L.（1988年）《生物化学杂志》263卷，9630 - 9634页）表明，小麦胚芽提取物中某些蛋白质合成起始因子的含量不足以使所有mRNA实现最佳翻译。在本研究中，采用定量酶联免疫吸附测定法来确定小麦胚芽提取物中真核起始因子（eIF）2、3、4A、4F和（异）4F的含量，以及40S核糖体亚基和延伸因子（EF）1α和2的含量。EF - 1α的含量最高（约占总蛋白的5%），而eIF - 4F的含量最低（约占总蛋白的0.03%）。这些因子和核糖体的微摩尔含量如下：EF - 1α为34；EF - 2为5.2；eIF - 2为1.5；eIF - 3为0.7；eIF - 4A为3.0，eIF - 4F为0.09；eIF - （异）4F为0.8；40S核糖体亚基为3.2。这些因子与40S核糖体亚基的摩尔比分别约为：EF - 1α为11:1，EF - 2为1.6:1，eIF - 2为0.45:1，eIF - 3为0.2:1，eIF - 4A为0.9:1，eIF - 4F为0.03:1，eIF - （异）4F为0.25:1。这些发现有力地表明，起始因子的浓度，特别是那些mRNA与核糖体结合所需的因子，可能在调节细胞内mRNA的翻译中起主要作用。
