Identification of spacer tRNA genes in individual ribosomal RNA transcription units of Escherichia coli.

Transfer RNA genes ("spacer tRNA genes") are present in the spacer region between 16S and 23S rRNA genes in Escherichia coli. We have analyzed spacer tRNA genes carried by seven rRNA operons with different chromosomal locations. Six of these were isolated on plasmids and one on a transducing phage. We found that, in addition to the two previously identified genes for tRNA2Glu and tRNAIIle, there is a spacer tRNA gene which codes for tRNAIBAla. Of the seven rRNA operons studied, three had both tRNAIBAla and tRNAIIle genes, and the remaining four had the tRNA2Glu gene in their spacers. In addition, genes for tRNAIAsp were found near the distal ends of two different rRNA operons.