Regulation of ribosomal protein synthesis in Escherichia coli

The kinetics of synthesis of ribosomal, nonribosomal, and total protein, and of ribosomal ribonucleic acid (RNA), were measured in Escherichia coli during a shift-up involving a doubling of specific growth rate. The increase in ribosomal protein synthesis was not accompanied by a corresponding decrease in non-ribosomal protein synthesis. Thus, the average rate of protein synthesis per ribosome increased after the shift. The increase did not occur by an increase in polypeptide chain growth rates. The average growth periods of ribosomal and nonribosomal proteins did not change after a shift, and were constant in cells in balanced growth over a wide range of specific growth rates. The average growth period for ribosomal protein was twice that for nonribosomal protein. The fraction of ribosomes in polyribosomes was found to increase after the shift, accounting for the increase in ribosomal protein synthesis and in protein synthesis per ribosome. These results show that ribosomal protein synthesis is regulated by control of initiation of either transcription or translation of ribosomal protein messenger RNA, by some means other than availability of free ribosomes. If the messenger for ribosomal protein is ribosomal RNA, the conclusions can be extended to apply to regulation of ribosomal RNA synthesis. In support of this, it is shown that ribosomal RNA and ribosomal protein synthesis are closely coordinated during a shift.