Tehfe Ali, Roseshter Talia, Wei Yulong, Xia Xuhua
Department of Biology, University of Ottawa, 30 Marie Curie, P.O. Box 450, Station A, Ottawa, ON K1N 6N5, Canada.
Ottawa Institute of Systems Biology, University of Ottawa, Ottawa, ON K1H 8M5, Canada.
Microorganisms. 2021 Mar 17;9(3):620. doi: 10.3390/microorganisms9030620.
encodes a key transcription factor that transmits the unfolded protein response (UPR) from the endoplasmic reticulum (ER) to the nucleus and regulates downstream UPR genes in . In response to the accumulation of unfolded proteins in the ER, Ire1p oligomers splice pre-mRNA () via a non-conventional process and allow the spliced () to be translated efficiently. However, leaky splicing and translation of may occur in non-UPR cells to induce undesirable UPR. To control accidental UPR activation, multiple fail-safe mechanisms have been proposed to prevent leaky splicing and translation and to facilitate rapid degradation of translated Hac1p and Hac1p. Among proposed regulatory mechanisms is a degron sequence encoded at the 5' end of the intron that silences Hac1p expression. To investigate the necessity of an intron-encoded degron sequence that specifically targets Hac1p for degradation, we employed publicly available transcriptomic data to quantify leaky splicing and translation in UPR-induced and non-UPR cells. As expected, we found that is only efficiently spliced into and efficiently translated into Hac1p in UPR-induced cells. However, our analysis of ribosome profiling data confirmed frequent occurrence of leaky translation of regardless of UPR induction, demonstrating the inability of translation fail-safe to completely inhibit Hac1p production. Additionally, among 32 yeast surveyed, the degron sequence is highly conserved by yeast but is poorly conserved by all other yeast species. Nevertheless, the degron sequence is the most conserved intron segment in yeasts. These results suggest that the degron sequence may indeed play an important role in mitigating the accumulation of Hac1p to prevent accidental UPR activation in the yeast.
编码一种关键转录因子，该因子将未折叠蛋白反应（UPR）从内质网（ER）传递至细胞核，并调节下游的UPR基因。响应内质网中未折叠蛋白的积累，Ire1p寡聚体通过非常规过程剪接前体mRNA（），并使剪接后的（）能够高效翻译。然而，在非UPR细胞中可能会发生的渗漏剪接和翻译，从而诱导不良的UPR。为了控制意外的UPR激活，人们提出了多种故障安全机制，以防止渗漏的剪接和翻译，并促进翻译后的Hac1p和Hac1p的快速降解。在提出的调控机制中，有一种位于内含子5'端编码的降解子序列，可使Hac1p表达沉默。为了研究特异性靶向Hac1p进行降解的内含子编码降解子序列的必要性，我们利用公开可用的转录组数据来量化UPR诱导细胞和非UPR细胞中的渗漏剪接和翻译。正如预期的那样，我们发现只有在UPR诱导的细胞中才有效地剪接成并有效地翻译成Hac1p。然而，我们对核糖体分析数据的分析证实，无论是否诱导UPR，都会频繁发生的渗漏翻译，这表明翻译故障安全机制无法完全抑制Hac1p的产生。此外，在调查的32种酵母中，降解子序列在酵母中高度保守，但在所有其他酵母物种中保守性较差。尽管如此，降解子序列是酵母中最保守的内含子片段。这些结果表明，降解子序列可能确实在减轻Hac1p的积累以防止酵母中意外的UPR激活方面发挥重要作用。
