Ribosomal proteins produced in excess are degraded by the ubiquitin-proteasome system.
Ribosomal proteins produced in excess are degraded by the ubiquitin-proteasome system.
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DOI：
10.1091/mbc.e16-05-0290
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发表时间：
2016-09-01
影响因子：
3.3
通讯作者：
Deshaies RJ
中科院分区：
文献类型：
--
作者：
Sung MK;Reitsma JM;Sweredoski MJ;Hess S;Deshaies RJ
酵母中核糖体蛋白的过度表达是通过细胞核和/或核核中未组装核糖体蛋白的泛素化以及蛋白酶体依赖性降解来防止的。蛋白酶体的短暂抑制会导致多种核糖体蛋白在不溶性部分的强烈积累，这表明这是一种普遍现象。核糖体组装是消耗大量细胞资源的重要过程。在酿酒酵母中，核糖体蛋白不能过量产生，因为过量的蛋白质会被迅速降解。然而，负责任的质量控制（QC）机制仍然缺乏特征。在这里，我们证明了酵母小核糖体亚基和大核糖体亚基的多种蛋白质的过表达受到抑制。从质粒中过表达的Rpl26可以在核核和核质中检测到，但它在很大程度上不能组装成核糖体并迅速降解。然而，如果内源性RPL26位点被删除，质粒编码的RPL26组装成核糖体并定位到细胞质中。化学和遗传扰动研究表明，过度表达的核糖体蛋白被泛素-蛋白酶体系统降解，而不是通过自噬。蛋白酶体的抑制导致多种内源性核糖体蛋白以不溶性聚集体的形式积累，这与这种QC机制在没有核糖体蛋白过表达的情况下的运作一致。我们的研究表明，未能组装成核糖体的核糖体蛋白与组装好的核糖体蛋白迅速区分开来，并在核室内泛素化和降解。
Overexpression of ribosomal proteins in yeast is prevented by ubiquitination of unassembled ribosomal proteins in the nucleus and/or nucleolus followed by proteasome-dependent degradation. Brief inhibition of proteasome causes strong accumulation of multiple ribosomal proteins in an insoluble fraction, suggesting that this is a general phenomenon. Ribosome assembly is an essential process that consumes prodigious quantities of cellular resources. Ribosomal proteins cannot be overproduced in Saccharomyces cerevisiae because the excess proteins are rapidly degraded. However, the responsible quality control (QC) mechanisms remain poorly characterized. Here we demonstrate that overexpression of multiple proteins of the small and large yeast ribosomal subunits is suppressed. Rpl26 overexpressed from a plasmid can be detected in the nucleolus and nucleoplasm, but it largely fails to assemble into ribosomes and is rapidly degraded. However, if the endogenous RPL26 loci are deleted, plasmid-encoded Rpl26 assembles into ribosomes and localizes to the cytosol. Chemical and genetic perturbation studies indicate that overexpressed ribosomal proteins are degraded by the ubiquitin–proteasome system and not by autophagy. Inhibition of the proteasome led to accumulation of multiple endogenous ribosomal proteins in insoluble aggregates, consistent with the operation of this QC mechanism in the absence of ribosomal protein overexpression. Our studies reveal that ribosomal proteins that fail to assemble into ribosomes are rapidly distinguished from their assembled counterparts and ubiquitinated and degraded within the nuclear compartment.