GENETIC & MOLECULAR STUDIES OF NEMATODE MRNA DEGRADATION

真核生物mRNAs的稳定水平由它们的合成和降解的相对速度决定。虽然我们对转录调控的分子机制知道很多，但相比之下，我们对mRNA降解的了解还很粗略。信使核糖核酸的稳定性是构成基因和调控基因表达的重要控制点。单个mRNAs的衰变是由特定的顺式作用元件和反式作用因子的相互作用决定的。顺式作用元件控制它们所在的mRNAs的衰变，而反式作用因子则与这些元件和其他细胞过程，特别是翻译装置相互作用。许多对信使核糖核酸衰变很重要的顺式作用序列已经被定义，但是这些元件如何与它们的反式作用因子一起完成选择性信使核糖核酸的周转还知之甚少。大多数信使核糖核酸的周转与翻译密切相关。这一点在无意义突变的mRNAs中尤为明显。含有提前终止密码子的mRNA在所有被测试的真核生物中都是不稳定的，包括人类。我们将在秀丽线虫体内研究这种现象，称之为“无意义介导的mRNA衰变”(NMD)。影响七个不同基因(SMG-1到SMG-7)中的任何一个的功能丧失突变可以消除整个动物的NMD。因此，SMG基因编码NMD所需的反式作用因子。我们的工作旨在回答三个一般性问题：SMG基因产物是什么？他们与什么互动？野生型线虫NMD的天然靶点是什么？我们的方法结合了对SMG基因及其编码蛋白的遗传、分子和生化研究。我们的长期目标是了解mRNA周转的分子机制和NMD的生物学作用。我们的实验通过识别NMD所需的蛋白质，描述它们在细胞中的生化关联，并研究SMG基因在正常基因表达中的作用，为这些目标做出了贡献。NMD是一种普遍现象，并导致某些人类遗传病的严重程度。了解线虫NMD的发病机制和SMG基因的功能将有助于了解这些疾病和其他疾病的病因。

The steady-state levels of eukaryotic mRNAs are dictated by their relative rates of synthesis and degradation. While we know a great deal about molecular mechanisms of transcriptional control, our understanding of mRNA degradation is sketchy by comparison. mRNA stability is an important control point for both constitutive and regulated gene expression. Decay of individual mRNAs is determined by the interplay of specific cis-acting elements and trans-acting factors. Cis-acting elements control decay of mRNAs in which they reside, while trans-acting factors interact with those elements and with other cellular processes, especially the translational apparatus. Numerous cis-acting sequences important for mRNA decay have been defined, but how these elements, together with their trans-acting factors, accomplish selective mRNA turnover is poorly understood. Most mRNA turnover is intimately coupled to translation. This is particularly clear in the case of nonsense mutant mRNAs. mRNAs that contain premature stop codons are unstable in all eukaryotes tested, including humans. We will study this phenomenon, termed "nonsense-mediated mRNA decay" (NMD) in the nematode Caenorhabditis elegans. Loss-of-function mutations affecting any of seven different genes (smg-1 through smg-7) eliminate NMD throughout the animal. Thus, smg genes encode trans-acting factors required for NMD. Our work is designed to answer three general questions: What are the smg gene products? With what do they interact? What are the natural targets of NMD in wild-type nematodes? Our methods combine genetic, molecular, and biochemical investigations of smg genes and their encoded proteins. Our long-range goals are to understand the molecular mechanisms of mRNA turnover and the biological roles of NMD. Our experiments contribute to these goals by identifying proteins that are required for NMD, describing their biochemical associations in the cell, and investigating the role of smg genes in normal gene expression. NMD is a universal phenomenon and contributes to the severity of certain human genetic diseases. Understanding the mechanisms of NMD and the functions of smg genes in C. elegans will contribute to understanding the etiology of these and other diseases.