Identification of a bifunctional enzyme MnmC involved in the biosynthesis of a hypermodified uridine in the wobble position of tRNA

The gene encoding the bifunctional enzyme MnmC that catalyzes the two last steps in the biosynthesis of 5-methylaminomethyl-2-thiouridine (mnm(5)S(2)U) in tRNA has been previously mapped at about 50 min on the Escherichia coli K12 chromosome, but to date the identity of the corresponding enzyme has not been correlated with any of the known open reading frames (ORFs). Using the protein fold-recognition approach, we predicted that the 74-kDa product of the yfcK ORF located at 52.6 min and annotated as putative peptidase comprises a methyltransferase domain and a FAD-dependent oxidoreductase domain. We have cloned, expressed, and purified the YfcK protein and demonstrated that it catalyzes the formation of mnm(5) s(2)U in tRNA. Thus, we suggest to rename YfcK as MnmC.