Heterogeneity of ribosomal populations in Escherichia coli cells grown in different media

Summary In order to establish whether ribosomes exhibit heterogeneity with respect to their protein pattern in vivo, E. coli cells were grown in rich or minimal medium and labeled with ¹⁴C and ³H amino acid mixture, respectively. After harvesting, the cells from the different media were mixed, the differently labeled ribosomes isolated and the ribosomal proteins separated. For each protein the ratio of ¹⁴C to ³H was determined and used as an indication of whether differences exist in ribosomal populations synthesized under different growth conditions.With respect to their ratio the ribosomal proteins can be classified as follows: Many of the proteins have a ratio of 1, i. e. they are present in the same amount in both preparations. The ratios for about 30% of the proteins differ only slightly from 1 whereas three proteins namely S6, S21 and L12 have ratios of 2.5 and 3.1 respectively. This means that ribosomal populations isolated from cells grown in rich medium contain these three proteins in two to three fold greater amounts compared to those synthesized in minimal medium.The relevance of these results with respect to the occurrence of heterogeneous ribosomal populations in vivo is discussed.Paper Nr. 36 on Ribosomal Proteins. Preceding paper is by H. J. Weber, Mol. Gen. Genetics 119, 233–248 (1972).