tRNA Genes in rRNA Operons of Escherichia coli

Abstract

In Escherichia coli, there are at least seven (Kenerley et al. 1977), and probably only seven (Kiss et al. 1977), rRNA operons located at different sites in the chromosome. Seven different rRNA operons have been isolated on hybrid plasmids (Kenerley et al. 1977) or on λ specialized transducing phages (Deonier et al. 1974; Lindahl et al. 1975; Jørgensen 1976; Jørgensen and Fiil 1976; Yamamoto and Nomura 1976). Early kinetic studies and investigations with the 30S precursor had indicated that each operon consisted of genes for all three rRNA species, transcribed in the order 16S-23S-5S (for review, see Nomura et al. 1977). In the course of examining the individual operons isolated in this laboratory and elsewhere, we have shown that there are tRNA genes located in all seven E. coli rRNA transcription units (Lund et al. 1976; Ikemura and Nomura 1977; Morgan et al. 1977). We have found that all rRNA operons have tRNA genes located between 16S and 23S rRNA genes. In addition, some operons have tRNA genes located at their distal ends (Morgan et al. 1978). In this discussion, we will summarize the evidence that tRNA genes are located in rRNA operons and comment on the significance of this discovery.

ISOLATION OF rRNA TRANSCRIPTION UNITS
Several E. coli rRNA operons were isolated on λ specialized transducing phages (Deonier et al. 1974; Lindahl et al. 1975; Jørgensen 1976; Jørgensen and Fiil 1976; Yamamoto and Nomura 1976). These phages contain rRNA operons from four regions of the chromosome (rrnB, rrnC, rrnD,...