Control of Gene Expression in the Biosynthesis of Mitochondrial Ribosomes

尽管核糖体在原核细胞和真核细胞中具有普遍性，但我们对核糖体的结构、功能和合成的大部分知识都是通过对细菌核糖体的深入研究而发展起来的，主要是在大肠杆菌中。与细菌不同，真核细胞在细胞质、叶绿体和线粒体中维持着不同的核糖体来合成蛋白质。一个重要的研究目标是了解真核核糖体的特征，这些核糖体代表着真核细胞对复杂基因组组织和亚细胞比较的特殊适应。酿酒酵母是一个分析单个细胞内细胞器和细胞质核糖体的肥沃的实验系统。几个实验室正在研究酵母细胞质核糖体，我们的目标是提供关于酵母线粒体核糖体及其组成的补充信息。酵母中线粒体翻译系统的主要功能是为内膜的能量传递复合体产生少量的亚单位。为了完成这一任务，两个核线粒体基因都被用来编码翻译装置所需的RNA和蛋白质。除了一个核糖体小亚基蛋白(VAR1)外，所有的核糖体蛋白都由60-70个不同的核基因编码。在我们描述的四个这样的基因中，MRP7和MRP20特别耐人寻味，因为它们编码的蛋白质分别与大肠杆菌50S核糖体亚基的EL27和EL23蛋白有关。MRP&Amp；和MRP20都是酵母中必不可少的蛋白质，有强有力的实验证据表明EL27与大肠杆菌核糖体的肽基转移酶中心之间存在着密切的物理联系。EL23是一种主要的rRNA结合蛋白，也可能位于肽vl转移酶中心附近。这项提案的研究目标是基于这样一种观点，即MRP7和MRP20与它们的细菌同行一样，很可能靠近核糖体的一个重要催化中心。我们打算使用分子遗传学和生物化学相结合的方法来：1)获得有关MRP7和/或MRP20的合成、结构和功能的更多信息。这项研究将为了解位于核糖体高度保守的功能区域的蛋白质的结构和功能提供新的见解。

Despite the universality of ribosomes in procaryotic and eucaryotic cells, the majority of our knowledge of their structure, function and synthesis has been developed through decades of intensive study of bacterial ribosomes, predominantly in E. coli. In contrast to bacteria, eucaryotic cell maintain distinctly different sets of ribosomes for protein synthesis in cytoplasm, chloroplasts, and mitochondria. An important research objective is to understand the features of eucaryotic ribosomes that represent special adaptations to complex genomic organization and subcellular comparmentalization for eucaryotic cells. The yeast Saccharomyces cerevisiae is a fertile experimental system for the analysis of both organellar and cytoplasmic ribosomes within a single cell. Several laboratories are studying yeast cytoplasmic ribosomes, our goal is to contribute complementary information about yeast mitochondrial ribosomes and their constituents. The principal function of the mitochondrial translation system in yeast is to produce a small number of subunits for the energy-transducing complexes of the inner membrane. To accomplish this task, both the nuclear mitochondrial genes are used to encode the requisite RNAs and proteins of the translational apparatus. With the exception of one protein of the small ribosomal subunit (VAR1), all of the ribosomal proteins are encoded by 60-70 different nuclear genes. Of the four such genes characterized by us MRP7 and MRP20 are particularly intriguing because they encode proteins that are related to the EL27 and EL23 proteins, respectively, of the E. coli 50S ribosomal subunit. Both MRP& and MRP20 are essential proteins in yeast, and there is strong experimental evidence for close physical proximity between EL27 and the peptidyltransferase center of the E. coli ribosome. EL23 is a primary rRNA binding protein, which may also be located near the peptidvltransferase center. The research objectives of this proposal are based on the contention that MRP7 and MRP20, like their bacterial counterparts, are likely to be close to an important catalytic center of the ribosome. We intend to use a combined molecular genetic and biochemical approach to : 1) gain additional information about the synthesis, structure, and function of the MRP7 and MRP20 or both. The research will provide new insight into the structure and function of proteins that are located in a highly conserved functional domain of the ribosome.