Level of rRNA, not tRNA, synthesis controls transcription of rRNA and tRNA operons in Escherichia coli.

We have recently proposed a model for the negative feedback control of rRNA and tRNA synthesis in Escherichia coli by products of rRNA operons or their derivatives (e.g., nontranslating ribosomes) (S. Jinks-Robertson, R.L. Gourse, and M. Nomura, Cell 33:865-876, 1983). In this paper, we examined the following questions. (i) Are the spacer tRNAs carried within rRNA operons the products responsible for the regulation of rRNA and tRNA transcription? (ii) Are tRNAs capable of regulating their own syntheses? We measured tRNA accumulations in cells containing plasmids with intact or defective rRNA operons or with tRNA operons. From the results obtained, we conclude that neither the tRNAs encoded within rRNA operons nor the tRNAs encoded in non-rRNA operons are capable of controlling rRNA or tRNA transcription. Therefore, the products responsible for the initial step leading to rRNA and tRNA regulation are rRNAs (or their derivatives).