ANALYSIS OF THE SHUTOFF OF RIBOSOMAL-RNA PROMOTERS IN ESCHERICHIA-COLI UPON ENTERING THE STATIONARY-PHASE OF GROWTH

Most bacterial RNA consists of stable RNA which is composed of rRNA an d tRNA. We have followed by primer extension analysis the level of rib osomal RNA synthesis along the growth phases of a cell culture. A shar p drop in rRNA synthesis was observed upon the transition from the exp onential to the stationary phase of growth. Our results demonstrate th at an effective shut-off of rRNA synthesis occurs also in the absence of ppGpp. Mutations in the host factors Fis and H-NS, which are known to regulate rrn P1 promoters, did not affect the shut-off process of r ibosomal RNA promoters. We also tested the effect of RpoS, the sigma f actor known to induce a number of genes in the stationary phase. It wa s shown that the host factors Fis, H-NS and RpoS do not play a major r ole in the regulation of the shut-off process of rRNA synthesis. The r esults presented demonstrate that the rate of rRNA synthesis provides a sensitive measure of the growth phase of the bacterial culture.