Ribosomal protein synthesis during and after amino acid starvation in relaxed and stringent bacteria

Abstract

The production of ribosomal protein during amino acid starvation and during the recovery from amino acid starvation has been investigated in RC rel and RC str strains of Escherichia coli. Within 15 seconds of restoration of the required amino acid to a previously starved RC rel strain, the proportion of total protein synthesis devoted to ribosomal protein is twice as high as during exponential growth. During the subsequent recovery, this proportion falls with a half-life of six to eight minutes to the value characteristic of exponential growth. This initial rise in proportion of protein synthesized pertains to all, or most, of the species of ribosomal protein. During recovery of an amino acid-starved RC str strain, however, the proportion of protein synthesis devoted to ribosomal protein is only slightly higher than during exponential growth. During starvation for a required amino acid, there proceeds a residual protein synthesis at a rate about 5% of that of exponential growth, in both RC rel and RC str strains. In a starved RC str strain the proportion of that protein synthesis devoted to ribosomal protein is less than half as great as the corresponding proportion during exponential growth. By contrast, in a starved RC rel strain, the proportion of that protein synthesis devoted to ribosomal protein is more than twice as great as the corresponding proportion during exponential growth. It is to be noted, however, that the starved RC rel strain does not produce the individual species of ribosomal protein in the same relative amounts as during exponential growth, but instead produces a few protein species at a very high relative rate. The state of the rel locus therefore affects not only the synthesis of ribosomal RNA under amino acid starvation, but also the synthesis of ribosomal protein.