Institute of Biochemistry and Biotechnology, General Biochemistry, Martin Luther University Halle-Wittenberg, Halle, Germany.
EMBO J. 2011 Jan 5;30(1):90-103. doi: 10.1038/emboj.2010.283. Epub 2010 Nov 16.
The nanos (nos) mRNA encodes the posterior determinant of the Drosophila embryo. Translation of the RNA is repressed throughout most of the embryo by the protein Smaug binding to Smaug recognition elements (SREs) in the 3' UTR. Translation is locally activated at the posterior pole by Oskar. This paper reports that the SREs govern the time- and ATP-dependent assembly of an exceedingly stable repressed ribonucleoprotein particle (RNP) in embryo extract. Repression can be virtually complete. Smaug and its co-repressor Cup as well as Trailer hitch and the DEAD box protein Me31B are part of the repressed RNP. The initiation factor eIF4G is specifically displaced, and 48S pre-initiation complex formation is inhibited. However, later steps in translation initiation are also sensitive to SRE-dependent inhibition. These data confirm several previously untested predictions of a current model for Cup-dependent repression but also suggest that the Cup model by itself is insufficient to explain translational repression of the nos RNA. In the embryo extract, recombinant Oskar relieves translational repression and deadenylation by preventing Smaug's binding to the SREs.
纳米（nos）mRNA 编码果蝇胚胎的后决定因素。在大多数胚胎中，RNA 的翻译通过 Smaug 蛋白与 3'UTR 中的 Smaug 识别元件（SRE）结合而受到抑制。Oskar 在后端极激活翻译。本文报道 SRE 控制在胚胎提取物中时间和 ATP 依赖性组装极其稳定的受抑制核糖核蛋白颗粒（RNP）。抑制作用几乎可以完全实现。Smaug 及其共抑制因子 Cup 以及 Trailer hitch 和 DEAD 盒蛋白 Me31B 都是受抑制 RNP 的一部分。起始因子 eIF4G 被特异性取代，48S 起始前复合物的形成受到抑制。然而，翻译起始的后续步骤也对 SRE 依赖性抑制敏感。这些数据证实了当前 Cup 依赖性抑制模型的几个以前未经测试的预测，但也表明 Cup 模型本身不足以解释 nos RNA 的翻译抑制。在胚胎提取物中，重组 Oskar 通过防止 Smaug 与 SRE 结合来解除翻译抑制和去腺苷酸化。
