Team Translation and Folding, Université de Rennes 1, UMR CNRS 6290 IGDR, Campus de Beaulieu, 35042 Rennes Cedex, France.
Université de Rennes 1, EA 1254, Campus de Beaulieu, 35042 Rennes Cedex, France.
J Mol Biol. 2014 Jan 23;426(2):377-88. doi: 10.1016/j.jmb.2013.09.035. Epub 2013 Oct 2.
During protein synthesis, many translating ribosomes are bound together with an mRNA molecule to form polysomes (or polyribosomes). While the spatial organization of bacterial polysomes has been well studied in vitro, little is known about how they cluster when cellular conditions are highly constrained. To better understand this, we used electron tomography, template matching, and three-dimensional modeling to analyze the supramolecular network of ribosomes after induction of translational pauses. In Escherichia coli, we overexpressed an mRNA carrying a polyproline motif known to induce pausing during translation. When working with a strain lacking transfer-messenger RNA, the principle actor in the "trans-translation" rescuing system, the cells survived the hijacking of the translation machinery but this resulted in a sharp modification of the ribosomal network. The results of our experiments demonstrate that single ribosomes are replaced with large amounts of compacted polysomes. These polysomes are highly organized, principally forming hairpins and dimers of hairpins that stack together. We propose that these spatial arrangements help maintain translation efficiency when the rescue systems are absent or overwhelmed.
在蛋白质合成过程中，许多正在翻译的核糖体与 mRNA 分子结合在一起形成多核糖体（或多聚核糖体）。虽然细菌多核糖体的空间组织已在体外得到很好的研究，但对于它们在细胞条件受到高度限制时如何聚集却知之甚少。为了更好地理解这一点，我们使用电子断层扫描、模板匹配和三维建模来分析诱导翻译暂停后核糖体的超分子网络。在大肠杆菌中，我们过表达了一种携带多脯氨酸基序的 mRNA，该基序已知在翻译过程中会引起暂停。当使用缺乏转移信使 RNA 的菌株时，该菌株是“转译转译”拯救系统的主要作用者，细胞能够在翻译机制被劫持后存活下来，但这导致核糖体网络发生了急剧的改变。我们实验的结果表明，单个核糖体被大量紧凑的多核糖体所取代。这些多核糖体高度组织化，主要形成发夹和发夹二聚体，彼此堆叠。我们提出，当拯救系统不存在或过载时，这些空间排列有助于维持翻译效率。
