GENETIC & MOLECULAR STUDIES OF NEMATODE MRNA DEGRADATION

真核生物mrna的稳态水平是由它们的合成和降解的相对速率决定的。虽然我们对转录控制的分子机制了解很多，但相比之下，我们对mRNA降解的理解还很粗略。mRNA的稳定性是组成基因和调控基因表达的重要控制点。单个mrna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mrna的衰变，而反式作用因子与这些元件和其他细胞过程，特别是翻译装置相互作用。已经定义了许多对mRNA衰变很重要的顺式作用序列，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mRNA转换却知之甚少。大多数mRNA的周转与翻译密切相关。这在无义突变mrna的情况下尤为明显。含有过早终止密码子的mrna在包括人类在内的所有真核生物中都是不稳定的。我们将研究这种现象，称为“无义介导的mRNA衰变”（NMD）在线虫秀丽隐杆线虫。影响七种不同基因（smg-1到smg-7）中的任何一种的功能丧失突变都会消除整个动物的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：什么是smg基因产物？它们与什么相互作用？NMD在野生型线虫中的天然靶点是什么？我们的方法结合了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转换的分子机制和NMD的生物学作用。我们的实验通过鉴定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，有助于实现这些目标。NMD是一种普遍现象，导致某些人类遗传疾病的严重程度。了解秀丽隐杆线虫NMD的机制和smg基因的功能将有助于了解这些疾病和其他疾病的病因学。

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.