Genetic mapping and cloning of the gene (trmC) responsible for the synthesis of tRNA (mnm5s2U)methyltransferase in Escherichia coli K12.

The trmC gene, responsible for the formation of 5-methylaminomethyl-2-thiouridine (mnm5s2U) from 2-thiouridine, present in the first position in the anticodon of some tRNAs, has been located at 50.5 min on the Escherichia coli K12 chromosome. Results from transductional mapping suggest that the trmC gene is located counter-clockwise of aroC. A ColE1 hybrid plasmid carrying the aroC+, trmC+ and hisT+ genes was isolated, and the gene order was established, by subcloning, to be hisT-trmC-aroC. The trmC gene is located 1.9 kb from the aroC gene. Two mutations (trmC1 and trmC2) were shown to be recessive, suggesting that the trmC gene is the structural gene for the tRNA-(mnm5s2U)methyltransferase.