Wolf Andrew S, Grayhack Elizabeth J
Department of Biochemistry and Biophysics, School of Medicine and Dentistry, University of Rochester, Rochester, New York 14642, USA.
Department of Biochemistry and Biophysics, School of Medicine and Dentistry, University of Rochester, Rochester, New York 14642, USA Center for RNA Biology, University of Rochester, Rochester, New York 14642, USA.
RNA. 2015 May;21(5):935-45. doi: 10.1261/rna.049080.114. Epub 2015 Mar 19.
Quality control systems monitor and stop translation at some ribosomal stalls, but it is unknown if halting translation at such stalls actually prevents synthesis of abnormal polypeptides. In yeast, ribosome stalling occurs at Arg CGA codon repeats, with even two consecutive CGA codons able to reduce translation by up to 50%. The conserved eukaryotic Asc1 protein limits translation through internal Arg CGA codon repeats. We show that, in the absence of Asc1 protein, ribosomes continue translating at CGA codons, but undergo substantial frameshifting with dramatically higher levels of frameshifting occurring with additional repeats of CGA codons. Frameshifting depends upon the slow or inefficient decoding of these codons, since frameshifting is suppressed by increased expression of the native tRNA(Arg(ICG)) that decodes CGA codons by wobble decoding. Moreover, the extent of frameshifting is modulated by the position of the CGA codon repeat relative to the translation start site. Thus, translation fidelity depends upon Asc1-mediated quality control.
质量控制系统会监测并在某些核糖体停滞处终止翻译，但目前尚不清楚在这些停滞处停止翻译是否真的能阻止异常多肽的合成。在酵母中，核糖体在精氨酸CGA密码子重复序列处发生停滞，即使是两个连续的CGA密码子也能使翻译减少多达50%。保守的真核生物Asc1蛋白通过内部的精氨酸CGA密码子重复序列限制翻译。我们发现，在没有Asc1蛋白的情况下，核糖体在CGA密码子处继续翻译，但会发生大量的移码，并且随着CGA密码子额外重复，移码水平会显著升高。移码取决于这些密码子的缓慢或低效解码，因为通过摆动解码识别CGA密码子的天然tRNA(Arg(ICG))表达增加会抑制移码。此外，移码的程度受CGA密码子重复序列相对于翻译起始位点位置的调节。因此，翻译保真度取决于Asc1介导的质量控制。
