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. N-6-threonylcarbamoyladenosine (t(6)A) 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. t(6)A and its derivatives have pleiotropic functions in protein synthesis including aminoacylation, decoding and translocation. We previously discovered a cyclic form of t(6)A (ct(6)A) as a chemically labile derivative of t(6)A in tRNAs from bacteria, fungi, plants and protists. Here, we report 2-methylthio cyclic t(6)A (ms(2)ct(6)A), a novel derivative of ct(6)A found in tRNAs from Bacillus subtilis, plants and Trypanosoma bru-cei. InB. subtilis and T. brucei, ms(2)ct(6)A disappeared and remained to be ms(2)t(6)A and ct(6)A by depletion of tcdA and mtaB homologs, respectively, demonstrating that TcdA and MtaB are responsible for biogenesis of ms(2)ct(6)A.