Fine-tuned regulation of protein biosynthesis is crucial for cellular fitness and became even more vital when cellular and organismal complexity increased during the course of evolution. In order to cope with this augmented demand for translation control, eukaryal ribosomes have gained extensions both at the ribosomal protein and rRNA levels. Here we analyze the functional role of ES27L, an rRNA expansion segment in the large ribosomal subunit of Saccharomyces cerevisiae. Deletion of the b-arm of this expansion segment, called ES27Lb, did not hamper growth during optimal conditions, thus demonstrating that this 25S rRNA segment is not inherently crucial for ribosome functioning. However, reductive stress results in retarded growth and rendered unique protein sets prone to aggregation. Lack of ES27Lb negatively affects ribosome-association of known co-translational N-terminal processing enzymes which in turn contributes to the observed protein aggregation. Likely as a compensatory response to these challenges, the truncated ribosomes showed re-adjusted translation of specific sets of mRNAs and thus fine-tune the translatome in order to re-establish proteostasis. Our study gives comprehensive insight into how a highly conserved eukaryal rRNA expansion segment defines ribosomal integrity, co-translational protein maturation events and consequently cellular fitness.

中文翻译：

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rRNA扩展区段27Lb调节酵母核糖体的因子募集能力并塑造蛋白质组。

蛋白质生物合成的精细调节对于细胞适应性至关重要，而在进化过程中，当细胞和生物体的复杂性增加时，调节就变得尤为重要。为了应付对翻译控制的这种增加的需求，真核核糖体在核糖体蛋白和rRNA水平上都得到了扩展。在这里，我们分析了酿酒酵母大核糖体亚基中的rRNA扩展片段ES27L的功能作用。在最佳条件下，删除此扩展片段的b-臂，即ES27Lb，不会妨碍生长，因此表明该25S rRNA片段对于核糖体功能并非固有地至关重要。然而，还原性应激导致生长迟缓，并且使独特的蛋白质集易于聚集。ES27Lb的缺乏会对已知的共翻译N末端加工酶的核糖体缔合产生负面影响，进而有助于观察到的蛋白质聚集。可能作为对这些挑战的补偿性反应，截短的核糖体显示出重新调节的特定mRNA组的翻译，因此微调了翻译组，以重新建立蛋白稳态。我们的研究为高度保守的真核rRNA扩增片段如何定义核糖体完整性，共翻译蛋白成熟事件以及因此的细胞适应性提供了全面的见解。截短的核糖体显示出重新调节了特定mRNA的翻译，因此微调了翻译组，以重新建立蛋白稳态。我们的研究为高度保守的真核rRNA扩增片段如何定义核糖体完整性，共翻译蛋白成熟事件以及因此的细胞适应性提供了全面的见解。截短的核糖体显示出重新调节了特定mRNA的翻译，因此微调了转位组以重新建立蛋白稳态。我们的研究为高度保守的真核rRNA扩增片段如何定义核糖体完整性，共翻译蛋白成熟事件以及因此的细胞适应性提供了全面的见解。