Minich W B, Ovchinnikov L P
Institute of Protein Research, Russian Academy of Sciences, Pushchino, Moscow Region.
Biochimie. 1992 May;74(5):477-83. doi: 10.1016/0300-9084(92)90088-v.
Polyribosomal and free mRNPs from rabbit reticulocytes were isolated and characterized. Translation of mRNPs was studied in the rabbit reticulocyte and wheat germ cell-free systems. Both classes of mRNPs were active in rabbit reticulocyte lysates. However, considerable differences between mRNPs and mRNA have been revealed. High concentrations of mRNA in the form of mRNP did not inhibit protein biosynthesis, whereas the same amounts of deproteinized mRNA caused inhibition of this process. Polyribosomal mRNPs and deproteinized mRNA, but not free mRNPs, are active in the wheat germ cell-free translation system. Translation of free mRNPs in this system can be restored by addition of 0.5 M KCl-wash of rabbit reticulocyte ribosomes. These results suggest the existence of a special repressor/activator regulatory system which controls mRNA distribution between free mRNPs and polyribosomes in rabbit reticulocytes. This regulatory system should include: i) a translation repressor associated with mRNA within free mRNPs, preventing its translation; and ii) a translation activator associated with ribosomes, overcoming the effect of the repressor. Both classes of cytoplasmic mRNPs contain a major 50 kDa protein (p50). The content of this protein per mol of mRNA in free mRNPs is twice as much as in polyribosomal ones. The method of p50 isolation has been developed and some properties of this protein were investigated. It has been shown that small amounts of p50 stimulate, whereas high amounts inhibit mRNA translation. We suggest that p50 has a dual role in protein biosynthesis. In polyribosomal mRNPs (p50:mRNA approximately 2:1, mol/mol), this protein promotes the translation process.(ABSTRACT TRUNCATED AT 250 WORDS)
从兔网织红细胞中分离并鉴定了多核糖体和游离的信使核糖核蛋白（mRNP）。在兔网织红细胞和麦胚无细胞体系中研究了mRNP的翻译。两类mRNP在兔网织红细胞裂解物中均具有活性。然而，已揭示出mRNP与信使核糖核酸（mRNA）之间存在显著差异。高浓度的mRNP形式的mRNA不会抑制蛋白质生物合成，而相同量的脱蛋白mRNA则会抑制这一过程。多核糖体mRNP和脱蛋白mRNA在麦胚无细胞翻译体系中具有活性，但游离mRNP无活性。在该体系中，通过添加经0.5M氯化钾洗涤的兔网织红细胞核糖体可恢复游离mRNP的翻译。这些结果表明存在一种特殊的阻遏物/激活物调节系统，该系统控制兔网织红细胞中游离mRNP和多核糖体之间的mRNA分布。这种调节系统应包括：i）与游离mRNP内的mRNA相关的翻译阻遏物，阻止其翻译；ii）与核糖体相关的翻译激活物，克服阻遏物效应。两类细胞质mRNP均含有一种主要的50千道尔顿蛋白（p50）。游离mRNP中每摩尔mRNA的该蛋白含量是多核糖体中该蛋白含量的两倍。已开发出p50的分离方法并研究了该蛋白的一些特性。结果表明，少量的p50会刺激mRNA翻译，而大量的p50则会抑制mRNA翻译。我们认为p50在蛋白质生物合成中具有双重作用。在多核糖体mRNP中（p50:mRNA约为2:1，摩尔/摩尔），该蛋白促进翻译过程。（摘要截短于250字）
