Molecular Biology Program, Memorial Sloan Kettering Cancer Center, New York, NY 10065, USA.
Gerstner Sloan Kettering Graduate School of Biomedical Sciences, New York, NY 10065, USA.
Nucleic Acids Res. 2023 Apr 24;51(7):3094-3115. doi: 10.1093/nar/gkad063.
Inorganic phosphate is an essential nutrient acquired by cells from their environment. Here, we characterize the adaptative responses of fission yeast to chronic phosphate starvation, during which cells enter a state of quiescence, initially fully reversible upon replenishing phosphate after 2 days but resulting in gradual loss of viability during 4 weeks of starvation. Time-resolved analyses of changes in mRNA levels revealed a coherent transcriptional program in which phosphate dynamics and autophagy were upregulated, while the machineries for rRNA synthesis and ribosome assembly, and for tRNA synthesis and maturation, were downregulated in tandem with global repression of genes encoding ribosomal proteins and translation factors. Consistent with the transcriptome changes, proteome analysis highlighted global depletion of 102 ribosomal proteins. Concomitant with this ribosomal protein deficit, 28S and 18S rRNAs became vulnerable to site-specific cleavages that generated temporally stable rRNA fragments. The finding that Maf1, a repressor of RNA polymerase III transcription, was upregulated during phosphate starvation prompted a hypothesis that its activity might prolong lifespan of the quiescent cells by limiting production of tRNAs. Indeed, we found that deletion of maf1 results in precocious death of phosphate-starved cells via a distinctive starvation-induced pathway associated with tRNA overproduction and dysfunctional tRNA biogenesis.
无机磷酸盐是细胞从其环境中获得的必需营养物质。在这里,我们描述了裂殖酵母对慢性磷酸盐饥饿的适应反应,在此期间,细胞进入静止状态,最初在补充磷酸盐后 2 天完全可逆,但在 4 周的饥饿过程中逐渐失去活力。对 mRNA 水平变化的时程分析显示出一个一致的转录程序,其中磷酸盐动态和自噬被上调,而 rRNA 合成和核糖体组装以及 tRNA 合成和成熟的机制与核糖体蛋白和翻译因子编码基因的全局抑制同时下调。与转录组变化一致,蛋白质组分析突出了 102 个核糖体蛋白的全面耗竭。伴随着这种核糖体蛋白缺陷,28S 和 18S rRNAs 变得容易受到特异性切割,产生暂时稳定的 rRNA 片段。在磷酸盐饥饿期间,RNA 聚合酶 III 转录的抑制剂 Maf1 上调的发现促使人们提出了一个假设,即它的活性可能通过限制 tRNA 的产生来延长静止细胞的寿命。事实上,我们发现 maf1 的缺失会导致磷酸盐饥饿细胞过早死亡,这是一种通过与 tRNA 过量产生和功能失调的 tRNA 生物发生相关的独特饥饿诱导途径。