Autogenous and post-transcriptional regulation of Escherichia coli RNA polymerase synthesis in vitro

Summary

The in vitro synthesis of Escherichia coli RNA polymerase β and β′ subunits is repressed by either holoenzyme or α₂β complex. The level of mRNA synthesized in this system, from the genes encoding ribosomal protein L7/12 (rplL) and RNA polymerase ββ′ subunits (rpoBC) was separately determined by DNA-RNA hybridization using the plasmids, pLOO and pLBC, each containing rplL and rplL plus rpoBC, respectively, as DNA probes. Although the synthesis of β and β′ polypeptides was repressed by exogenous addition of the autorepressors, the amount of rpoBC mRNA increased in parallel with the total RNA synthesis. Thus, the relative concentration of rpoBC mRNA stayed at a constant level. Based on the simultaneous determination of both protein and mRNA, it was concluded that the autogenous regulation of RNA polymerase β and β′ subunit synthesis operates post-transcriptionally, presumably at the translational level. Similarly, glycerol inhibition of β and β′ subunit synthesis was also found to be operative at post-transcriptional step(s). In contrast, the rifampicin induction of β and β′ subunit synthesis is due to both the increased transcription of rpoBC genes and the relaxation of the autogenous repression.

The present study also implied that the majority of the transcription of the rpoBC operon terminates between rplL and rpoB genes. The difference in the intracellular content of ribosomal protein L7/12 and RNA polymerase ββ′ subunits might be attributed, at least in part, to transcriptional attenuation.