Graduate School of Natural Science and Technology, Okayama University, Okayama, Japan.
Research Core for Interdisciplinary Sciences, Okayama University, Okayama, Japan.
Sci Rep. 2016 Aug 19;6:31774. doi: 10.1038/srep31774.
High-level expression of a protein localized to an intracellular compartment is expected to cause cellular defects because it overloads localization processes. However, overloads of localization processes have never been studied systematically. Here, we show that the expression levels of green fluorescent proteins (GFPs) with localization signals were limited to the same degree as a toxic misfolded GFP in budding yeast cells, and that their high-level expression caused cellular defects associated with localization processes. We further show that limitation of the exportin Crm1 determined the expression limit of GFP with a nuclear export signal. Although misfolding of GFP with a vesicle-mediated transport signal triggered endoplasmic reticulum stress, it was not the primary determinant of its expression limit. The precursor of GFP with a mitochondrial targeting signal caused a cellular defect. Finally, we estimated the residual capacities of localization processes. High-level expression of a localized protein thus causes cellular defects by overloading the capacities of localization processes.
高水平表达定位于细胞内隔室的蛋白质预计会导致细胞缺陷，因为它使定位过程过载。然而，定位过程的过载从未被系统地研究过。在这里，我们表明，具有定位信号的绿色荧光蛋白 (GFP) 的表达水平与芽殖酵母细胞中有毒的错误折叠 GFP 一样受到限制，并且它们的高水平表达会导致与定位过程相关的细胞缺陷。我们进一步表明，核输出蛋白 Crm1 的输出限制决定了具有核输出信号的 GFP 的表达限制。虽然具有囊泡介导运输信号的 GFP 的错误折叠引发内质网应激，但它不是其表达限制的主要决定因素。具有线粒体靶向信号的 GFP 前体导致细胞缺陷。最后，我们估计了定位过程的剩余能力。因此，高水平表达定位于蛋白质的蛋白质通过使定位过程的能力过载而导致细胞缺陷。
