Cloning of the promoters of an Escherichia coli rRNA gene New experimental system to study the regulation of rRNA transcription

The promoters of the rrnB gene of Escherichia coli have been cloned on a multicopy, pBR322-derived plasmid by deleting most of the structural part of rrnB and fusing the terminators of the gene immediately to the promoters. Several further deletions were constructed to vary the promoter-terminator distance, destroy or damage selectively any of the promoters or terminators, and vary the distance btween the two pairs of P 1 P 2 and P 3 P 4 promoters. All these transcription signals were shown to function on the plasmids in vitro and in vivo. The truncated in vivo transcription products initiated at the P 1 and P 2 promoters of the recombinant plasmids were found to be stable, and the accumulated transcripts could be easily distinguished from the chromosome-coded rRNA. This provides a convenient experimental system to study the regulation of rRNA biosynthesis.