ISOLATED P2 RIBOSOMAL-RNA PROMOTERS OF ESCHERICHIA-COLI ARE STRONG PROMOTERS THAT ARE SUBJECT TO STRINGENT CONTROL

Ribosomal RNA synthesis in Escherichia coli is under stringent control . The seven rRNA operons are highly conserved and are each transcribed from two tandem promoters, P1 and P2, which are located about 120 bas e-pairs apart. In exponentially growing cells the majority of the tran scripts are initiated at the P1 promoters. The P1 promoters are highly regulated, and are under stringent as well as growth rate controls. H ere we demonstrate that transcription from the rrnA P1 promoter dimini shes P2 expression. In the absence of P1, the P2 promoter acts as a ra ther strong promoter. Insertion of a transcription terminator between P1 and P2 eliminates the inhibition of P2 by P1, suggesting that the p hysical movement of RNA polymerase originating at P1 and progressing a long the P2 promoter is necessary for the interference process to take place. Similarly to P1, the solitary P2 promoter is subject to string ent control.