Stress-induced translation inhibition through rapid displacement of 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 RNA-protein interactome, without corresponding changes in RBP abundance. Consistent with general translation shutdown, ribosomal proteins contacting the mRNA showed decreased RNA-association. Among translation components, RNA-association was most reduced for initiation factors involved in 40S scanning (eIF4A, eIF4B, and Ded1), indicating a common mechanism of translational repression. In unstressed cells, eIF4A, eIF4B, and Ded1 primarily targeted the 5′-ends of mRNAs. Following glucose withdrawal, 5’-binding was abolished within 30sec, explaining the rapid translation shutdown, but mRNAs remained stable. Heat shock induced progressive loss of 5’ RNA-binding by initiation factors over ~16min. Translation shutoff provoked selective 5′-degradation of mRNAs, particularly for translation-related factors, mediated by Xrn1. 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。本研究针对葡萄糖饥饿与热休克胁迫，对酿酒酵母中RNA结合蛋白的全局动态变化进行了分析。两种胁迫均快速引发RNA-蛋白质互作组的重塑，而RNA结合蛋白的丰度未发生相应变化。与整体翻译停滞的现象一致，与mRNA结合的核糖体蛋白的RNA结合能力出现下降。在翻译相关组分中，参与40S亚基扫描的起始因子（eIF4A、eIF4B与Ded1）的RNA结合能力降幅最为显著，这提示存在一种共同的翻译抑制机制。在未受胁迫的细胞中，eIF4A、eIF4B与Ded1主要靶向mRNA的5'端区域。在葡萄糖剥夺后，这些起始因子的5'端结合活性在30秒内即完全消失，这解释了翻译快速停滞的原因，但mRNA本身仍保持稳定。热休克则会在约16分钟的时间内逐步导致起始因子丧失5'端RNA结合能力。翻译停滞会引发mRNA发生选择性5'端降解，这类降解尤其富集于翻译相关因子的mRNA，且由Xrn1介导。本研究结果揭示了胁迫条件下基因表达的翻译调控机制。