Gafny, R., Department of Cellular Biochemistry, Hebrew University, Hadassah Medical School, Jerusalem, Israel, Department of Virology, Agricultural Research Organization, Volcani Center, Bet-Dagan, 50250, Israel
Cohen, S., Department of Cellular Biochemistry, Hebrew University, Hadassah Medical School, Jerusalem, Israel
Nachaliel, N., Department of Cellular Biochemistry, Hebrew University, Hadassah Medical School, Jerusalem, Israel
Glaser, G., Department of Cellular Biochemistry, Hebrew University, Hadassah Medical School, Jerusalem, Israel

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 base-pairs apart. In exponentially growing cells the majority of the transcripts are initiated at the P1 promoters. The P1 promoters are highly regulated, and are under stringent as well as growth rate controls. Here we demonstrate that transcription from the rrnA P1 promoter diminishes P2 expression. In the absence of P1, the P2 promoter acts as a rather strong promoter. Insertion of a transcription terminator between P1 and P2 eliminates the inhibition of P2 by P1, suggesting that the physical movement of RNA polymerase originating at P1 and progressing along the P2 promoter is necessary for the interference process to take place. Similarly to P1, the solitary P2 promoter is subject to stringent control.