Role of attenuation in growth rate-dependent regulation of the S10 r-protein operon of E. coli.

We have investigated the transcription of the 11 gene S10 ribosomal protein operon of Escherichia coli under various growth conditions. The differential synthesis rate of structural gene message increases 2- to 2.5-fold immediately after a shift-up from glycerol minimal medium to glucose plus amino acids. After the initial increase, the transcription rate goes through several oscillations before reaching the new steady-state rate. By comparing the rates of transcription of leader and structural genes, we conclude that these oscillations are due predominantly to changes in the level of read-through at the S10 attenuator. This regulation of attenuation can account for most of the variations in protein synthesis from the S10 operon after a shift. We also measured the level of read-through in cells growing exponentially in different growth media. Over a 2.5-fold range in growth rates, the read-through changed less than 50%. Thus, regulation of attenuation cannot explain the growth-dependent regulation of ribosomal protein synthesis during steady-state growth. Apparently, additional mechanisms are required to control the expression of the S10 operon in exponentially growing cells.