Ribosomes slide on lysine-encoding homopolymeric A stretches
Ribosomes slide on lysine-encoding homopolymeric A stretches
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DOI：
10.7554/elife.05534
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发表时间：
2015-02-19
期刊：
影响因子：
7.7
通讯作者：
Green, Rachel
中科院分区：
文献类型：
--
作者：
Koutmou, Kristin S.;Schuller, Anthony P.;Green, Rachel
如果适当的trna足够丰富，同义密码子的蛋白质输出被认为是等效的。在这里，我们发现编码迭代赖氨酸密码子AAA或AAG的mrna对蛋白质合成的影响是不同的：在ORF中插入迭代AAA密码子比插入同义AAG密码子更能减少蛋白质的表达。大肠杆菌的动力学研究表明，差异蛋白的产生是由于在连续的aaa赖氨酸上暂停，然后核糖体在同聚A序列上滑动。细胞自由表达系统中的翻译表明，含有aaa密码子的报告子的输出减少是由于核糖体滑动后，帧外停止密码子的过早翻译终止。在真核生物中，这些过早终止事件针对mrna进行无义介导的衰变（NMD）。核糖体在同聚A序列上滑动的发现解释了生物信息学分析表明，连续的AAA密码子在基因编码序列中代表性不足。核糖体“滑动”代表了翻译过程中可能出现的一种意想不到的核糖体运动。
Protein output from synonymous codons is thought to be equivalent if appropriate tRNAs are sufficiently abundant. Here we show that mRNAs encoding iterated lysine codons, AAA or AAG, differentially impact protein synthesis: insertion of iterated AAA codons into an ORF diminishes protein expression more than insertion of synonymous AAG codons. Kinetic studies in E. coli reveal that differential protein production results from pausing on consecutive AAA-lysines followed by ribosome sliding on homopolymeric A sequence. Translation in a cell free-expression system demonstrates that diminished output from AAA-codon-containing reporters results from premature translation termination on out of frame stop codons following ribosome sliding. In eukaryotes, these premature termination events target the mRNAs for Nonsense-Mediated-Decay (NMD). The finding that ribosomes slide on homopolymeric A sequences explains bioinformatic analyses indicating that consecutive AAA codons are under-represented in gene-coding sequences. Ribosome 'sliding' represents an unexpected type of ribosome movement possible during translation.