Purification and Identification of Escherichia coli Ribosomal Proteins

Abstract

INTRODUCTION The complex nature of the protein moiety of E. coli ribosomes was at first revealed by Waller and Harris (1961). Starch gel electrophoresis resulted in the separation of more than twenty bands. Although these and later studies (Waller 1964) supported the hypothesis that there are many different proteins in E. coli ribosomes, uncertainty still existed for several years about the number of ribosomal proteins in each of the two subunits. This uncertainty was mainly due to the observation in other systems that the number of bands in gel electrophoresis was often much higher than the number of individual proteins. Aggregation and modification of proteins, e.g., by oxidation or by carbamylation in urea-containing buffers, can give rise to additional bands in polyacrylamide gel electrophoresis. To solve this problem, it became necessary to isolate all ribosomal proteins and, by chemical, physical and immunological characterization, to determine the exact number of individual proteins with a unique structure. Furthermore, purification and characterization of the ribosomal proteins are important prerequisites for an understanding at the molecular level of the structure and function of ribosomes and their components. This chapter presents an outline of the different methods used in the extraction and purification of ribosomal proteins. Based on the characterization of the proteins, the question of how many of the isolated proteins have unique and individual structures is answered. Furthermore, it is discussed whether all proteins which can be isolated from a population of ribosomes are “true” ribosomal proteins, and finally, a correlation of ribosomal...