Translation of CGA codon repeats in yeast involves quality control components and ribosomal protein L1.
Translation of CGA codon repeats in yeast involves quality control components and ribosomal protein L1.
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DOI：
10.1261/rna.039446.113
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发表时间：
2013-09
期刊：
影响因子：
--
通讯作者：
Grayhack EJ
中科院分区：
文献类型：
--
作者：
Letzring DP;Wolf AS;Brule CE;Grayhack EJ
众所周知，在出芽酵母中，CGA密码子重复序列的翻译是低效的。本文研究了翻译效率低下的原因，结果显示出意想不到的复杂性，表明CGA密码子对翻译的抑制至少是由两个独立的缺陷引起的。酵母中CGA密码子重复序列的翻译效率低下，导致mRNA切割产物的表达和产生的剂量依赖性降低，表明核糖体停滞。在这里，我们使用遗传学和翻译抑制剂来了解核糖体如何响应CGA重复。我们发现CGA密码子重复序列导致一个截断的多肽，该多肽被Ltn1降解，Ltn1是一种E3泛素连接酶，参与不间断的衰变，尽管Ltn1的删除并不能改善CGA重复序列下游的表达。CGA密码子下游第318个残基的表达，而不是第4个残基的表达，通过ASC1或HEL2的缺失而得到改善，这之前与多碱基序列的翻译抑制有关。因此，CGA重复序列的翻译可能导致核糖体停滞并利用已知的质量控制系统。paromomycin是一种氨基糖苷，可以放松解码特异性，从而改善CGA重复序列在氨基酸4处下游的表达。如果天然tRNAArg（ICG）高表达，Paromomycin就没有作用，这与CGA密码子无法有效解码的观点一致，部分原因可能是同源tRNAArg（ICG）被排斥。此外，CGA重复序列下游的表达通过RPL1B失活得到改善，RPL1B是编码普遍保守的核糖体蛋白L1的两个基因之一。rpl1b-Δ和paromomycin或tRNAArg（ICG）对CGA解码的影响是加性的，这表明rpl1b-Δ突变体通过增加tRNAArg（ICG）的接受度以外的方式抑制CGA抑制。因此，CGA的低效解码可能涉及翻译中至少两个独立的缺陷。
It has been known that translation of CGA codon repeats in budding yeast is inefficient. This paper examines the reasons for inefficient translation, and the findings indicate unexpected complexity revealing that inhibition of translation by CGA codons results from at least two independent defects. Translation of CGA codon repeats in the yeast Saccharomyces cerevisiae is inefficient, resulting in dose-dependent reduction in expression and in production of an mRNA cleavage product, indicative of a stalled ribosome. Here, we use genetics and translation inhibitors to understand how ribosomes respond to CGA repeats. We find that CGA codon repeats result in a truncated polypeptide that is targeted for degradation by Ltn1, an E3 ubiquitin ligase involved in nonstop decay, although deletion of LTN1 does not improve expression downstream from CGA repeats. Expression downstream from CGA codons at residue 318, but not at residue 4, is improved by deletion of either ASC1 or HEL2, previously implicated in inhibition of translation by polybasic sequences. Thus, translation of CGA repeats likely causes ribosomes to stall and exploits known quality control systems. Expression downstream from CGA repeats at amino acid 4 is improved by paromomycin, an aminoglycoside that relaxes decoding specificity. Paromomycin has no effect if native tRNAArg(ICG) is highly expressed, consistent with the idea that failure to efficiently decode CGA codons might occur in part due to rejection of the cognate tRNAArg(ICG). Furthermore, expression downstream from CGA repeats is improved by inactivation of RPL1B, one of two genes encoding the universally conserved ribosomal protein L1. The effects of rpl1b-Δ and of either paromomycin or tRNAArg(ICG) on CGA decoding are additive, suggesting that the rpl1b-Δ mutant suppresses CGA inhibition by means other than increased acceptance of tRNAArg(ICG). Thus, inefficient decoding of CGA likely involves at least two independent defects in translation.
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