Identification of two new promoters probably involved in the transcription of a ribosomal RNA gene of Escherichia coli.

The DNA sequence in the region preceding the rrnB gene of Escherichia coli was determined up to the 1821st nucleotide upstream from the beginning of the sequence coding for mature 16 S rRNA. In vitro transcription experiments indicated the presence of two new promoters in this region, located more than 1 kb upstream from the known P1 and P2 promoters of rrnB. Previous electron microscopic studies demonstrated that these sites bind RNA-polymerase very strongly. In vitro transcription, starting at these sites reads through the entire region into the rrnB gene without termination. A similar uninterrupted transcription into rrnB in vivo can be demonstrated by S1-mapping, and by fusing the DNA containing the new promoters (but not P1 and P2) to the lacZ gene. Thus it seems likely that these promoters (P3 and P4) belong functionally to the rrnB gene and play some role in its regulation of expression.