RNA-POLYMERASE ACTIVITY MAY REGULATE TRANSCRIPTION INITIATION AND ATTENUATION IN THE RPLKAJLRPOBC OPERON IN ESCHERICHIA-COLI

The relationship between global RNA transcription capacity and transcript initiation, attenuation, and stability in the rplKAJLrpoBC operon of Escherichia coli has been examined. The rplKAJLrpoBC operon encodes in order the four large ribosome subunit proteins, L11, L1, L10, and L12, and the two large beta and beta' subunits of RNA polymerase. Operon transcripts are initiated at two promoters, P(L11) and P(L10). The L12-beta intergenic space contains a transcription attenuator which, during balanced growth, terminates about 80% of the transcripts exiting the L12 gene; the remaining transcripts read through into the beta and beta' encoding genes. The capacity for global transcription initiation was modulated using a strain carrying a temperature-sensitive, initiation-defective mutation in rpoC. Following a shift to 39-degrees-C, the global transcription initiation capacity was reduced to about one-half the level at 30-degrees-C. This partial restriction resulted in a decrease in the stability of distal beta mRNA, whereas the stability of proximal L11-L1 and L10-L12 mRNA was not changed. Measurements of the synthesis rates of L11-L1, L10-L12, and beta mRNAs relative to total RNA synthesis indicated that this operon was selectively transcribed when the initiation capacity of RNA polymerase was limited. The synthesis rates of L11-L1 and L10-L12 mRNA increased about 2-fold, whereas the synthesis rate of beta mRNA increased nearly 5-fold. The relative transcription of other ribosome component genes and the alpha subunit gene exhibited only a modest increase during the partial restriction. Protection from S1 nuclease was used to demonstrate that the preferential transcription within the operon of beta mRNA was the consequence of active regulation of termination-antitermination at the attenuator structure in the L12-beta intergenic space. These results demonstrate that global transcription capacity may be an important parameter in determining both initiation and attenuation of transcription of the rplKAJLrpoBC ribosomal protein-RNA polymerase operon.