Differential stringent control of the tandem E. coli ribosomal RNA promoters from the rrnA operon expressed in vivo in multicopy plasmids

The tandem P₁, P₂ promoter region of the rrnA ribosomal operon has been fused to the t₁, t₂ terminator region of the rrnB operon in pBR322 plasmid derivatives. This deletes most internal RNA structural elements ordinarily processed out of ribosomal operon transcripts. In vivo as well as in vitro transcripts arising from both promoters terminate predominately in the t₁ terminator region about 40 base pairs beyond the mature rrnB 5S RNA gene. Stringent control of the P₁ and P₂ promoted transcripts has been assessed in vivo. In these plasmid fusions, the upstream (P₁) promoter activity was subject to stringent control, while the downstream (P₂) promoter activity was inhibited by amino acid starvation in both stringent and relaxed hosts. A plasmid with an additional deletion of the P₂ region also showed stringent regulation of the P₁ promoter.