Kabat D, Chappell M R
J Biol Chem. 1977 Apr 25;252(8):2684-90.
Translation of messenger ribonucleic acids for alpha- and beta-globin chains was analyzed in an mRNA-dependent fractionated protein-synthesizing system derived from rabbit reticulocytes. The alpha/beta chain synthesis ratio is highly dependent on the concentration of unfractionated globin mRNAs; the ratio is 1.5 at low mRNA concentration and declines to 0.03 at a high concentration. Several lines of evidence support the conclusion that this effect is caused by competitive binding of the messengers to an initiation factor which preferentially associates with the beta-mRNA. Such a discriminating factor is present in the 0.5 M KCl wash fraction from ribosomes and it elutes from a diethylaminoethyl-cellulose column between 0.10 and 0.21 M KCl. Studies using purified preparations of initiation factors suggest that IF-M3 and IF-M4 may act synergistically to produce the activity of the discriminating initiation factor. Although the discriminating factor is required for translation of both messengers, its apparent binding constant to beta-mRNA is 50 times larger than to alpha-mRNA. The concentration of discriminating factor-mRNA complex does not limit the overall rate of protein synthesis in this cell-free system. Nevertheless, the relative effectiveness of different messengers is determined by the relative concentrations of their complexes with the discriminating factor.
在源自兔网织红细胞的依赖信使核糖核酸（mRNA）的分级分离蛋白质合成系统中，对α-和β-珠蛋白链的信使核糖核酸（mRNA）的翻译进行了分析。α/β链合成比率高度依赖于未分级的珠蛋白mRNA的浓度；在低mRNA浓度下该比率为1.5，在高浓度下则降至0.03。几条证据支持这样的结论，即这种效应是由信使与一种起始因子的竞争性结合引起的，该起始因子优先与β-mRNA结合。这种具有区分作用的因子存在于核糖体的0.5M氯化钾洗涤级分中，并且它从二乙氨基乙基纤维素柱上在0.10至0.21M氯化钾之间洗脱。使用纯化的起始因子制剂进行的研究表明，IF-M3和IF-M4可能协同作用以产生具有区分作用的起始因子的活性。尽管两种信使的翻译都需要这种具有区分作用的因子，但其与β-mRNA的表观结合常数比对α-mRNA的大50倍。在这个无细胞系统中，具有区分作用的因子-mRNA复合物的浓度并不限制蛋白质合成的总体速率。然而，不同信使的相对有效性是由它们与具有区分作用的因子的复合物的相对浓度决定的。
