Functions of 4.5S RNA in the bacterial cell

描述(申请人提供)：信号识别颗粒(SRP)是一种在进化上高度保守的核糖核蛋白复合体，其功能是将蛋白质靶向生物膜。由于大肠杆菌含有一个由FFH蛋白和4.5S RNA组成的“最小”SRP，它为理解易位机制如何在所有活细胞中发挥作用提供了一个有吸引力的系统。了解细菌SRP功能的RNA成分的作用是复杂的，因为它对细胞生长和参与蛋白质合成至关重要。由于很少有研究了解4.5S RNA的序列决定因素在体内如何影响其功能，因此人们对RNA为什么是膜蛋白定位和蛋白质翻译机制的重要组成部分知之甚少。我们研究的长期目标是确定4.5S RNA作为SRP的一个组成部分如何将蛋白质靶向内膜，并通过其与延伸因子G的相互作用在翻译中发挥作用。我们建议对4.5S RNA进行系统的遗传特征分析，以确定该分子的结构对其活性的贡献，并探讨RNA在蛋白质合成和膜蛋白定位中的功能。我们对4.5S RNA的细胞作用缺乏了解是很重要的，因为它阻碍了我们在分子水平上充分描述蛋白质定位和多肽合成的基本过程。由于SRP RNA的进化保守性很高，到目前为止在所有生命物种中都发现了同源物，我们也将更好地理解这种RNA物种在所有生命系统中的功能。尽管最近的工作主要集中在4.5S核糖核酸的体外分析上，包括生化特性和结构测定，但对4.5S S核糖核酸在体内的功能的了解一直滞后，部分原因是缺乏研究该分子的遗传系统。这些研究应该有助于改进表达和定位具有医学意义的膜蛋白的方法，并导致抗菌剂的鉴定。

DESCRIPTION (provided by applicant): The signal recognition particle (SRP) is a highly evolutionarily conserved ribonucleoprotein complex that functions to target proteins into biological membranes. Because E. coli contains a "minimal" SRP, consisting of the Ffh protein in association with a 4.5S RNA species, it provides an attractive system to understand how the translocation machinery functions in all living cells. Understanding the role of the RNA component of the bacterial SRP function is complicated by its essentiality for cell growth and its involvement in protein synthesis. Since few studies have been performed to understand how the sequence determinants of 4.5S RNA contribute to its function in vivo, little is known about why the RNA is an essential component of both the membrane protein localization and protein translation machinery. The long-term goal of our research is to determine how 4.5S RNA functions as a component of the SRP to target proteins to the inner membrane, and in translation by its interaction with elongation factor G. We propose to perform a systematic genetic characterization of 4.5S RNA to determine how the structure of this molecule contributes to its activity, and to probe the function of the RNA in both protein synthesis and membrane protein localization. Our lack of knowledge about the cellular roles of 4.5S RNA is significant in that it prevents us from fully describing the essential processes of protein localization and polypeptide synthesis on a molecular level. Due to the high evolutionary conservation of the SRP RNA, with homologues found in all living species examined to date, we will also better comprehend how this RNA species functions in all living systems. Although recent efforts have been placed largely on in vitro analysis of 4.5S RNA, including biochemical characterization and structural determinations, efforts to understand the function of 4.5 S RNA in vivo has lagged in part due to the lack of genetic systems for studying this molecule. These studies should contribute to improved methods to express and localize membrane proteins of medical importance, as well as lead to the identification of antimicrobial agents.