Kuperwasser Nicolas, Brogna Saverio, Dower Ken, Rosbash Michael
Howard Hughes Medical Institute, Department of Biology, Brandeis University, 415 South St., Waltham, MA 02454, USA.
RNA. 2004 Dec;10(12):1907-15. doi: 10.1261/rna.7132504.
Nonsense-mediated decay (NMD) is a eukaryotic regulatory process that degrades mRNAs with premature termination codons (PTCs). Although NMD is a translation-dependent process, there is evidence from mammalian systems that PTC recognition and mRNA degradation takes place in association with nuclei. Consistent with this notion, degradation of mammalian PTC-containing mRNAs occurs when they are bound by the cap binding complex (CBC) during a "pioneer" round of translation. Moreover, there are reports indicating that a PTC can trigger other nuclear events such as alternative splicing, abnormal 3' end processing, and accumulation of pre-mRNA at transcription sites. To examine whether a PTC can elicit similar nuclear events in yeast, we used RNA export-defective mutants to sequester mRNAs within nuclei. The results indicate that nuclear PTC-containing yeast RNAs are NMD insensitive. We also observed by fluorescent in situ hybridization that there was no PTC effect on mRNA accumulated at the site of transcription. Finally, we show that yeast NMD occurs minimally if at all on CBC-bound transcripts, arguing against a CBC-mediated pioneer round of translation in yeast. The data taken together indicate that there are no direct consequences of a PTC within the yeast nucleus.
无义介导的衰变（NMD）是一种真核生物调节过程，可降解带有提前终止密码子（PTC）的mRNA。尽管NMD是一个依赖翻译的过程，但来自哺乳动物系统的证据表明，PTC识别和mRNA降解与细胞核相关联。与此观点一致的是，当含有PTC的哺乳动物mRNA在“先驱”轮翻译过程中被帽结合复合物（CBC）结合时，就会发生降解。此外，有报道表明，PTC可引发其他核事件，如可变剪接、异常的3'端加工以及前体mRNA在转录位点的积累。为了研究PTC在酵母中是否能引发类似的核事件，我们使用了RNA输出缺陷型突变体将mRNA隔离在细胞核内。结果表明，细胞核内含有PTC的酵母RNA对NMD不敏感。我们还通过荧光原位杂交观察到，PTC对在转录位点积累的mRNA没有影响。最后，我们表明酵母NMD在与CBC结合的转录本上即使发生也极少发生，这与酵母中CBC介导的先驱轮翻译观点相悖。综合这些数据表明，酵母细胞核内的PTC没有直接后果。
