Protein Topography of Ribosomal Subunit from Escherichia coli

Abstract

INTRODUCTION The 70S ribosome of Escherichia coli contains 54 different proteins (see Wittmann, this volume). The ribosome may be considered as an organelle whose functional properties are determined by cooperative interactions among its RNA and protein components. There is evidence showing that many of the functional properties of ribosomes, i.e., the capacity to catalyze the specific reactions of peptide bond formation and GTP hydrolysis and to bind a number of protein and RNA ligands, are determined by ribosomal proteins. This does not mean that the role of ribosomal RNA should be ignored. It is nevertheless the aim of this article to summarize available evidence bearing primarily on the spatial arrangement of ribosomal proteins with respect to each other. To achieve this end, models have been constructed which depict the position of all the 30S proteins and half of the 50S ribosomal proteins. It is hoped that the models will prove to be a reasonable approximation of the subunit structures. However at the very least, the models provide a concise and graphic means of summarizing a vast amount of experimental evidence; moreover, they should provide a framework within which to design and correlate the results of future experiments. In order to simplify construction of models of both the 30S and 50S subunits, it has been assumed that all proteins are spheres of roughly equivalent size. This is patently untrue, since it is well established that the proteins range in size from approximately 9000 to 35,000 daltons (S1 excepted; the nomenclature of...