Chemical Structure of Bacterial Ribosomal Proteins

Abstract

INTRODUCTION The isolation of ribosomal proteins which is described in the preceding contribution has enabled chemical, physical and immunological studies to be made on the structure of these proteins. The chemical investigations to be summarized here include studies on the amino acid composition, isoelectric points, N-termini, peptide maps, isolation and analysis of tryptic peptides, and determination of the complete sequence of some proteins. By far the majority of these investigations were done on ribosomal proteins from E. coli and its mutants, but recently similar studies have begun on proteins from Bacillus stearothermophilus ribosomes. Furthermore, conclusions about the chemical structure of ribosomal proteins from numerous bacterial species can be drawn by comparative studies with electrophoretic and immunological methods. ESCHERICHIA COLI WILD TYPE Isoelectric Points It became evident from early electrophoretic studies on E. coli ribosomal proteins (Waller 1964; Leboy, Cox and Flaks 1964) that many of the proteins must be very basic. Determination of the isoelectric point for each of the proteins from E. coli ribosomes was possible by two-dimensional polyacrylamide gel electrophoresis at different pH values (Kaltschmidt 1971). About 70% of the proteins have isoelectric points of pH 10 and higher, whereas those of only three proteins, namely S6, L7 and L12, are at about pH 5. There is no significant difference between 30S and 50S proteins with respect to their isoelectric points. Amino Acid Compositions The basic nature of most E. coli ribosomal proteins is also reflected by their amino acid compositions. However, as it is not possible to...