Silva Ana Luísa, Pereira Francisco J C, Morgado Ana, Kong Jian, Martins Rute, Faustino Paula, Liebhaber Stephen A, Romão Luísa
Centro de Genética Humana, Instituto Nacional de Saúde Dr. Ricardo Jorge, 1649-016 Lisboa, Portugal.
RNA. 2006 Dec;12(12):2160-70. doi: 10.1261/rna.201406. Epub 2006 Oct 31.
Nonsense-mediated mRNA decay (NMD) is a surveillance mechanism that degrades mRNAs carrying premature translation termination codons. Generally, NMD is elicited if translation terminates >50-54 nucleotides (nt) upstream of an exon-exon junction. We have previously reported that human beta-globin mRNAs carrying 5'-proximal nonsense mutations (e.g., beta15) accumulate to normal levels, suggesting an exception to the "50-54-nt boundary rule." In the present report, we demonstrate that the strength of the UPF1-dependent NMD of mutant beta-globin mRNAs is specifically determined by the proximity of the nonsense codon to the initiation AUG. This conclusion is supported by a parallel effect of the short ORF size on NMD of nonsense-containing alpha-globin mRNAs. To determine whether the short-ORF effect on NMD response is conserved in heterologous transcripts, we assessed its effects on a set of beta-globin/triosephosphate isomerase (TPI) hybrid mRNAs and on the TPI mRNA. Our data support the conclusion that nonsense mutations resulting in a short ORF are able to circumvent the full activity of the canonical UPF1-dependent NMD pathway.
无义介导的mRNA降解（NMD）是一种监测机制，可降解携带提前翻译终止密码子的mRNA。一般来说，如果翻译在一个外显子-外显子连接上游>50-54个核苷酸（nt）处终止，就会引发NMD。我们之前报道过，携带5'-近端无义突变的人β-珠蛋白mRNA（例如β15）积累到正常水平，这表明存在“50-54-nt边界规则”的一个例外情况。在本报告中，我们证明了突变型β-珠蛋白mRNA的UPF1依赖性NMD的强度具体由无义密码子与起始AUG的接近程度决定。这一结论得到了短开放阅读框大小对含无义α-珠蛋白mRNA的NMD的平行影响的支持。为了确定短开放阅读框对NMD反应的影响在异源转录本中是否保守，我们评估了其对一组β-珠蛋白/磷酸丙糖异构酶（TPI）杂交mRNA和TPI mRNA的影响。我们的数据支持这样的结论，即导致短开放阅读框的无义突变能够规避经典的UPF1依赖性NMD途径的全部活性。
