Stress-induced condensation of mRNA and proteins into stress granules is conserved across eukaryotes, yet the function, formation mechanisms, and relation to well-studied conserved transcriptional responses remain largely unresolved. Stress-induced exposure of ribosome-free mRNA following translational shutoff is thought to cause condensation by allowing new multivalent RNA-dependent interactions, with RNA length and associated interaction capacity driving increased condensation. Here we show that, in striking contrast, virtually all mRNA species condense in response to multiple unrelated stresses in budding yeast, length plays a minor role, and instead, stress-induced transcripts are preferentially excluded from condensates, enabling their selective translation. Using both endogenous genes and reporter constructs, we show that translation initiation blockade, rather than resulting ribosome-free RNA, causes condensation. These translation initiation-inhibited condensates (TIICs) are biochemically detectable even when stress granules, defined as microscopically visible foci, are absent or blocked. TIICs occur in unstressed yeast cells, and, during stress, grow before the appearance of visible stress granules. Stress-induced transcripts are excluded from TIICs primarily due to the timing of their expression, rather than their sequence features. Together, our results reveal a simple system by which cells redirect translational activity to newly synthesized transcripts during stress, with broad implications for cellular regulation in changing conditions.

中文翻译：

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转录组范围内的 mRNA 浓缩先于应激颗粒形成并排除应激诱导的转录本

应激诱导的 mRNA 和蛋白质凝结成应激颗粒在真核生物中是保守的，但其功能、形成机制以及与经过充分研究的保守转录反应的关系在很大程度上仍未得到解决。翻译关闭后，应激诱导的无核糖体 mRNA 的暴露被认为通过允许新的多价 RNA 依赖性相互作用而引起凝结，其中 RNA 长度和相关的相互作用能力驱动凝结增加。在这里，我们发现，与此形成鲜明对比的是，几乎所有 mRNA 物种都会在芽殖酵母中响应多种不相关的应激而发生凝缩，长度起着次要作用，相反，应激诱导的转录物优先被排除在凝结物之外，从而实现它们的选择性翻译。使用内源基因和报告基因构建体，我们发现翻译起始阻断，而不是产生的无核糖体RNA，导致了缩合。即使当应力颗粒（定义为显微镜可见的焦点）不存在或被阻挡时，这些翻译起始抑制凝结物（TIIC）也可以通过生化方法检测到。 TIIC 发生在未受应激的酵母细胞中，并且在应激过程中，在可见的应激颗粒出现之前生长。应激诱导的转录本被排除在 TIIC 之外主要是因为它们的表达时间，而不是它们的序列特征。总之，我们的结果揭示了一个简单的系统，通过该系统，细胞在应激期间将翻译活性重定向到新合成的转录物，这对变化条件下的细胞调节具有广泛的影响。