Division of Biological Sciences, University of California, San Diego, CA, USA.
Department of Chemistry & Biochemistry, University of California, San Diego, CA, USA.
RNA Biol. 2022;19(1):636-649. doi: 10.1080/15476286.2022.2065784. Epub 2021 Dec 31.
Protein synthesis is energetically expensive and its rate is influenced by factors such as cell type and environment. Suppression of translation is a canonical response to stressful changes in the cellular environment. In particular, inhibition of the initiation step of translation has been highlighted as the key control step in stress-induced translational suppression as mechanisms that quickly suppress initiation are well-conserved. However, cells have evolved complex regulatory means to control translation apart from initiation. Here, we examine the role of the elongation step of translation in yeast subjected to acute glucose deprivation. The use of ribosome profiling and reporter assays demonstrated elongation rates slow progressively following glucose removal. We observed that ribosome distribution broadly shifts towards the downstream ends of transcripts after both acute and gradual glucose deprivation but not in response to other stressors. Additionally, on assessed mRNAs, a correlation existed between ribosome occupancy and protein production pre-stress but was lost after stress. These results indicate that stress-induced elongation regulation causes ribosomes to slow down and build up on a considerable proportion of the transcriptome in response to glucose withdrawal. Finally, we report ribosomes that built up along transcripts are competent to resume elongation and complete protein synthesis after readdition of glucose to starved cells. This suggests that yeast has evolved mechanisms to slow translation elongation in response to glucose starvation which do not preclude continuation of protein production from those ribosomes, thereby averting a need for new initiation events to take place to synthesize proteins. AUG: start codon, bp: base pair(s), CDS: coding sequence, CHX: cycloheximide, eEF2: eukaryotic elongation factor 2, LTM: lactimidomycin, nt: nucleotide, PGK1: 3-phosphoglycerate kinase, ribosomal biogenesis: ribi, RO: ribosome occupancy, RPF: ribosome protected fragment, TE: translational efficiency.
蛋白质合成的能量消耗很大，其合成速率受到细胞类型和环境等因素的影响。抑制翻译是细胞应对环境应激变化的一种典型反应。特别是，翻译起始步骤的抑制已被突出为应激诱导翻译抑制的关键控制步骤，因为快速抑制起始的机制在进化上是保守的。然而，细胞已经进化出了除起始之外控制翻译的复杂调节手段。在这里，我们研究了在酵母中急性葡萄糖饥饿时翻译延伸步骤的作用。核糖体图谱和报告基因测定的使用表明，葡萄糖去除后延伸速度逐渐减慢。我们观察到，在急性和逐渐的葡萄糖饥饿后，核糖体的分布广泛地向转录本的下游端转移，但在响应其他应激源时则没有。此外，在评估的 mRNA 上，核糖体占有率与应激前的蛋白质产生之间存在相关性，但在应激后则丢失。这些结果表明，应激诱导的延伸调节导致核糖体在葡萄糖缺失时在相当大比例的转录本上减速并积累。最后，我们报告说，沿着转录本积累的核糖体在饥饿细胞重新加入葡萄糖后有能力恢复延伸并完成蛋白质合成。这表明，酵母已经进化出了在葡萄糖饥饿时减缓翻译延伸的机制，这并不排除从那些核糖体上继续进行蛋白质的产生，从而避免需要新的起始事件来合成蛋白质。AUG：起始密码子，bp：碱基对，CDS：编码序列，CHX：环己酰亚胺，eEF2：真核延伸因子 2，LTM：乳酰胺霉素，nt：核苷酸，PGK1：3-磷酸甘油酸激酶，核糖体生物发生：ribi，RO：核糖体占有率，RPF：核糖体保护片段，TE：翻译效率。
