Genetic organization and transcription from the gene (trmA) responsible for synthesis of tRNA (uracil-5)-methyltransferase by Escherichia coli

The enzyme catalyzing the formation of 5-methyluridine (ribothymidine) in tRNA of Escherichia coli is tRNA (uracil-5)-methyltransferase (EC 2.1.1.35). A 2.8-kilobase EcoRI chromosomal DNA fragment contains trmA, the structural gene for this enzyme. Subcloning, transcription in vitro, Tn5 insertion mutagenesis, and transcriptional fusion experiments were performed to establish the gene organization of the trmA region on the E. coli chromosome. trmA is a monocistronic operon. The trmA promoter was localized by in vitro experiments, and the direction of transcription was shown to be counterclockwise on the standard E. coli K-12 chromosomal map. The level of transcription of trmA in vitro and the expression of protein in minicells equal those of the bla gene of plasmid pBR322.