van der Meer J P, Ganoza M C
Eur J Biochem. 1975 May;54(1):229-37. doi: 10.1111/j.1432-1033.1975.tb04132.x.
The mutant Escherichia coli strain, N4316, has a temperature-sensitive defect in a protein factor required for translation in vitro of bacteriophage f2 RNA. We have purified the normal counterpart of this factor from a wild-type strain, using as an assay its ability to restore the activity of mutant extracts at non-permissive temperature. Our final preparation is free of known initiation, propagation, and release factors, proving that the factor is a new component required for translation. The new factor has a molecular weight of 95000 with preliminary data suggesting a subunit structure. 70% of this protein is found in the soluble-cell fraction, the rest being associated with 70-S ribosomes. Kinetic analyses indicate that the factor acts early in translation. Expression of the defect is highly dependent on the Mg2+ concentration, no temperature-sensitivity being apparent at 15 mM Mg2+. At lower Mg2+ concentrations, the defect is expressed only with natural mRNAs such as f2 RNA, and not with artifical polymers such as poly(U). This specificity suggests that the factor may function in events coded by special sequences in the natural messengers
突变型大肠杆菌菌株N4316在噬菌体f2 RNA体外翻译所需的一种蛋白质因子中存在温度敏感缺陷。我们从野生型菌株中纯化了该因子的正常对应物，利用其在非允许温度下恢复突变提取物活性的能力进行检测。我们的最终制剂不含已知的起始、延伸和释放因子，证明该因子是翻译所需的一种新成分。这种新因子的分子量为95000，初步数据表明它具有亚基结构。该蛋白质的70%存在于可溶性细胞组分中，其余与70-S核糖体相关。动力学分析表明，该因子在翻译早期起作用。缺陷的表达高度依赖于Mg2+浓度，在15 mM Mg2+时没有明显的温度敏感性。在较低的Mg2+浓度下，缺陷仅在天然mRNA（如f2 RNA）中表达，而在人工聚合物（如聚尿苷酸）中不表达。这种特异性表明该因子可能在天然信使中的特殊序列编码的事件中发挥作用。
