Stress-induced translation inhibition through release of 40S scanning initiation factors

Cellular responses to environmental stress are frequently mediated by RNA-binding proteins (RBPs). Here, we examined global RBP dynamics in Saccharomyces cerevisiae in response to glucose starvation and heat shock. Each stress induced rapid remodeling of the protein:RNA interactome, without corresponding changes in RBP abundance. Consistent with translational shutdown, ribosomal proteins contacting the mRNA showed decreased RNA-association. Among translation components, in either stress RNA-association was most reduced for initiation factors involved in 40S scanning (eIF4A, eIF4B, and Ded1), indicating common mechanisms of translational repression. In unstressed cells, eIF4A, eIF4B, and Ded1 primarily targeted the 5′-ends of mRNAs. Following glucose withdrawal, mRNAs remained stable, but 5’-binding was abolished within 30sec, explaining the rapid translation shutdown. Heat shock induced progressive loss of 5’ RNA-binding by initiation factors over ~16min. Translation shutoff provoked 5’-degradation by Xrn1, selectively for mRNAs encoding translation-related factors. These results reveal mechanisms underlying translational control of gene expression during stress.细胞对环境胁迫的应答通常由RNA结合蛋白（RNA-binding proteins, RBPs）介导。本研究针对酿酒酵母（Saccharomyces cerevisiae）在葡萄糖饥饿与热激胁迫下的全局RBP动态变化展开分析。两种胁迫均可快速诱导蛋白质-RNA互作组发生重塑，而RBP的丰度并未出现相应变化。与翻译关闭的现象一致，与信使RNA（messenger RNA, mRNA）结合的核糖体蛋白其RNA结合能力出现下降。在翻译相关组分中，两种胁迫下参与40S亚基扫描的起始因子（eIF4A、eIF4B及Ded1）的RNA结合能力降幅最为显著，这表明翻译抑制存在共同的作用机制。在未受胁迫的细胞中，eIF4A、eIF4B及Ded1主要靶向mRNA的5'端。葡萄糖剥夺后，mRNA整体保持稳定，但上述起始因子的5'端结合活性在30秒内即完全丧失，这解释了翻译快速关闭的原因。热激则在约16分钟内逐步导致起始因子丧失mRNA 5'端结合能力。翻译关闭会引发Xrn1介导的5'端降解，且该过程选择性地作用于编码翻译相关因子的mRNA。上述研究结果揭示了胁迫过程中基因表达的翻译调控机制。