In vivo stability, maturation and relative differential synthesis rates of individual ribosomal proteins in Escherichia coli B/r

The relative differential synthesis rates² of individual ribosomal proteins (r-proteins) were determined for Escherichia coli B/r growing in succinate medium (growth rate, μ = 0.65 doublings per hour), glucose medium (μ = 1.36) and glucose-amino acids medium (μ = 1.90). These differential synthesis rates were found to increase co-ordinately with increasing bacterial growth rates; this implies that ribosomes from bacteria growing at different rates are homogeneous with respect to their protein composition (i.e. the stoichiometric amounts of the different r-proteins per ribosome are constant and independent of the bacterial growth rate). Following incorporation into ribosomes, the bulk of the r-proteins were found to be as stable as total protein. Only two r-proteins, S6 and S21, were less stable than total protein; their decay half-lives, measured in succinate and glucose-amino acids cultures, were estimated to be approximately 500 minutes. In addition, post-translational modification of proteins S18, L6 and L11 was observed and the possible relations between modification and in vivo ribosome assembly are discussed. Finally, evidence is presented suggesting that the coordinate production of r-proteins may result, in part, from a mechanism that degrades excess r-proteins that are not rapidly incorporated into ribosomal particles.     

Regulation of ribosomal protein synthesis in Escherichia coli B/r.

The differential synthesis rate of ribosomal protein (r-protein), alpha-r (synthesis rate of r-protein divided by synthesis rate of total protein), was measured during the cell division cycle. It was observed that alpha-r remained essentially constant and was not measurably affected by duplication of the r-protein gene cluster (i.e., str-spc region) during the process of chromosome replication. It was further observed that the rate of total protein synthesis and r-protein synthesis increased continuously and uniformly during the entire cell cycle. This gene dosage independence of the synthesis rate of r-protein was similar to that observed earlier for the synthesis of ribosomal ribonucleic acid (rRNA). These observations indicate that the synthesis rates of the protein and RNA components of the ribosome are coordinately balanced during the entire cell division cycle and are not significantly perturbed by duplication of the r-protein or rRNA genes. Furthermore, this balanced synthesis insures that neither free rRNA nor free r-protein accumulate in appreciable amounts during balanced growth.     

Synthesis of ribosomal proteins in merodiploid strains of Escherichia coli

Summary The regulation of the synthesis of r-proteins in Escherichia coli was investigated by increasing the dosage of the genes for a limited number of ribosomal proteins (r-proteins) using either transducing phage fus 3 (Lindahl et al. 1977) or rif ^d18 (Kirschbaum and Konrad 1973). During exponential growth the presence in the cell of either lysogenised transducing phage did not increase the rate of synthesis or degradation of any of the 31 r-proteins whose genes are duplicated. Experiments were also performed to determine whether r-protein synthesis during the period of unbalanced r-protein synthesis that follows nutritional enrichment was sensitive to an increase in gene dosage. Duplication of the 27 r-protein genes on fus 3 did not alter the rate of synthesis of any of the r-proteins after enrichment. However, gene dosage effects were detected for at least 3 of the r-proteins whose genes were duplicated of rif ^d18.     

The cell cycle in Escherichia coli B/r

Cell division and DNA synthesis were measured in synchronous cultures of E. coll B/r growing in glucose minimal medium at 37 °. The kinetic curves were analysed in order to find the variability of replication initiation, termination, and cell division events during the cell cycle. It is inferred that under the conditions used, cells begin to divide 17 min (D₀ = minimum D-period) after each termination of chromosome replication with a constant probability per unit of time (half-life = 4·5–6 min). This randomness produces an asymmetric frequency distribution of D-periods, similar but mirror-symmetric frequency distributions of initiation and termination periods, a symmetric, non-Gaussian distribution of interdivision intervals, and complex kinetic changes in the rate of DNA synthesis as a function of cell age. The results suggest that replication and division are precisely controlled with respect to mass accumulation, and the apparent variability of cell cycle events would only result from the use of the time of cell separation as a reference point for the definition of cell age rather than initiation or termination of replication.     

Plasmolysis of Escherichia coli B/r with Sucrose

Escherichia coli B/r cells were plasmolyzed in sucrose solutions and observed under phase contrast. The prevalence of plasmolysis under various conditions was noted, and the degree of plasmolysis was categorized as slight, extensive, or severe. The presence of ions reduced the prevalence of plasmolysis. Survival curves showed that extensive plasmolysis was not lethal to colony-forming ability.     

Genetic studies of the ribosomal proteins in Escherichia coli. 3. Compositions of ribosomal proteins in various strains of Escherichia coli

Summary The comparative chromatographic investigations into the ribosomal proteins of various strains of E. coli have demonstrated that most of the strains including three strains of E. coli subsp. communior had ribosomes with the same protein compositions (C-type). The ribosomes from strain B are different from the C-type ribosomes in having the specific 30-4 (B) component in place of 30-4 (B-type), while those from strains K 12 may be distinguished from the type-C ribosomes by the presence of the specific 30-7 (K) component in place of 30-7 (K-type) or, in addition to 30-7 (K), the presence of 30-9 (W3637) in place of 30-9 (K-3637 type). Two strains, IAM 1132 and IAM 1182, have R-type ribosomes, in which at least six 50s proteins and four 30s protein components are distinct from the corresponding protein components in the C-type ribosomes.