DIVERSITY IN THE NUMBERS,TYPES AND SEQUENCES OF TRNA'S

蛋白质合成依赖于一个复杂的细胞机器，包括转移RNA （tRNA）、氨基酰基tRNA合成酶、起始、延伸和释放因子，以及核糖体RNA （rRNA）和核糖体蛋白。由于翻译是一个基本的细胞过程，强稳定选择预计会影响其组成部分。然而，基因组测序项目的结果表明，尽管翻译的一般过程在整个进化过程中是保守的，但生物体以许多不同的方式保持准确和有效的蛋白质合成。特别是，在生物内部和生物之间，它们的trna的数量和类型以及序列和结构特征都存在意想不到的差异。因此，过渡器官的弹性显然比通常认为的要大。提出的实验是由这些观察激发的，旨在回答三个相关的问题。是什么机制导致了同工受体之间的序列变异？是什么机制使生物体在进化过程中失去“必需的”tRNA基因？细胞可耐受的tRNA功能损伤程度有多大？拟议的研究使用生化和遗传方法来回答这些问题。它将研究(i)反密码子在tRNA功能和进化中的作用；（ii）补偿tRNA基因损失的机制；（iii）细胞生存和生长所必需的tRNA功能水平。这些结果将阐明trna中在蛋白质合成过程中决定其氨基酸接受和提供功能的元件。此外，他们将阐明影响trna这些活性的翻译装置的特性。因此，结果将是有关的程度，不同的表型是从一个单一的基因型表达由于在细胞中的情况的一般问题。对这一现象的理解对于DNA序列信息的解释以及通过操纵翻译机制来控制细菌感染的一些策略的发展至关重要。

Protein synthesis depends on a complex cellular machine comprised of transfer RNA (tRNA), aminoacyl-tRNA synthetases, initiation, elongation, and release factors, as well as ribosomal RNA (rRNA) and ribosomal proteins. Because translation is an essential cellular process, strong stabilizing selection is expected to influence its components. However, results from the genome sequencing projects show that although the general process of translation is conserved throughout evolution, organisms maintain accurate and efficient protein synthesis in many different ways. In particular, there are unexpected differences within and among organisms in the numbers and types as well as in the sequence and structural features of their tRNAs. Thus there is apparently more resiliency in the transitional apparatus than is typically thought. The proposed experiments are motivated by these observations and are designed to answer three related questions. What are the mechanisms that account for sequence variation among isoacceptors? What are the mechanisms that allow organisms to lose "essential" tRNA genes during evolution? What is the extent of impairment in tRNA function that can be tolerated by the cell? The proposed research uses biochemical and genetic approaches to answer these questions. It will examine (i) the role of the anticodon in tRNA function and evolution; (ii) the mechanisms that compensate for tRNA gene loss; and (iii) the levels of tRNA function that are necessary for cell viability and growth. The results will elucidate elements in tRNAs that dictate their amino acid accepting and donating functions during protein synthesis. In addition, they will elucidate the properties of the translational apparatus that influence these activities of tRNAs. Thus the results will be pertinent to the general problem of the extent to which different phenotypes are expressed from a single genotype due to circumstances in the cell. An understanding of this phenomenon is critical to the interpretation of DNA sequence information and to the development of some strategies that have been proposed for controlling bacterial infections by manipulating the translation machinery.