Identification of 2-methylthio cyclic N6-threonylcarbamoyladenosine (ms2ct6A) as a novel RNA modification at position 37 of tRNAs

Transfer RNA modifications play pivotal roles in protein synthesis. N6-threonylcarbamoyladenosine (t6A) and its derivatives are modifications found at position 37, 3΄-adjacent to the anticodon, in tRNAs responsible for ANN codons. These modifications are universally conserved in all domains of life. t6A and its derivatives have pleiotropic functions in protein synthesis including aminoacylation, decoding and translocation. We previously discovered a cyclic form of t6A (ct6A) as a chemically labile derivative of t6A in tRNAs from bacteria, fungi, plants and protists. Here, we report 2-methylthio cyclic t6A (ms2ct6A), a novel derivative of ct6A found in tRNAs from Bacillus subtilis, plants and Trypanosoma brucei. In B. subtilis and T. brucei, ms2ct6A disappeared and remained to be ms2t6A and ct6A by depletion of tcdA and mtaB homologs, respectively, demonstrating that TcdA and MtaB are responsible for biogenesis of ms2ct6A.