Rps26 directs mRNA-specific translation by recognition of Kozak sequence elements

The “Kozak sequence”, immediately upstream of the start codon, regulates the translational efficiency of an mRNA. Nevertheless, how this sequence is recognized remains unexplored. Here, we describe a novel approach to separate two ribosome populations from the same cells and use this method, and RNA-seq, to identify the mRNAs bound to ribosomes with and without Rps26, a protein linked to the pathogenesis of Diamond Blackfan Anemia (DBA). These analyses reveal that Rps26 contributes to recognition of the Kozak sequence in well-translated mRNAs, and that Rps26-deficient ribosomes preferentially translate mRNA from select stress response pathways. Surprisingly, we demonstrate that exposure of cells to these stresses leads to the formation of Rps26-deficient ribosomes and to the translation of their targets. Thus, Rps26-deficient ribosomes play aberrant pathogenic roles in DBA as well as physiological roles in augmenting the well-characterized stress transcriptional response with a heretofore unknown translational stress response, thereby creating a feed forward loop in gene-expression.紧邻起始密码子上游的科扎克序列（Kozak sequence），可调控信使RNA（mRNA）的翻译效率。然而，该序列的识别机制仍未得到阐明。本研究报道了一种可从同一细胞中分离两种核糖体群体的全新方法，并结合该方法与RNA测序（RNA-seq），鉴定出与携带Rps26及不携带Rps26的核糖体结合的mRNA——Rps26是一种与戴布克凡贫血（Diamond Blackfan Anemia, DBA）发病机制相关的蛋白质。上述分析显示，Rps26参与识别高翻译效率mRNA中的科扎克序列，而缺乏Rps26的核糖体则优先翻译特定应激反应通路相关的mRNA。令人意外的是，本研究证实，细胞暴露于此类应激条件时，会形成缺乏Rps26的核糖体，并启动其靶mRNA的翻译程序。综上，缺乏Rps26的核糖体在戴布克凡贫血中发挥异常致病作用，同时可通过一种此前未知的翻译层面应激响应，强化已被充分研究的转录应激响应，由此在基因表达过程中形成一个前馈调控环路。