This family includes members such as TrmO (tRNA-methyltransferase O) also known as YaeB, which contains a single-sheeted beta-barrel structure. TrmO is an AdoMet-dependent methyltransferase responsible for m6t6A formation [1]. Its human homolog, is responsible for formation of m6t6A37 in cytoplasmic tRNASer. Lack of TrmO decreases attenuation activity of the thr operon, indicating that N6 methylation of m6t6A37 ensures efficient decoding of ACY codons [2]. In bacteria and eukaryotes, TrmO has a C-terminal domain containing the conserved DPRxxY motif. Where the Asp194 and Arg196 in this motif of E. coli TrmO are necessary for N6-methylation. However, no archaeal YaeB has a C-terminal domain containing the DPRxxY motif that is conserved in bacterial and mammalian TrmO homologs [1].

1: Discovery of the beta-barrel-type RNA methyltransferase responsible for N6-methylation of N6-threonylcarbamoyladenosine in tRNAs. Kimura S, Miyauchi K, Ikeuchi Y, Thiaville PC, Crecy-Lagard Vd, Suzuki T; Nucleic Acids Res. 2014;42:9350-9365. PMID:25063302

2: Identification of 2-methylthio cyclic N6-threonylcarbamoyladenosine (ms2ct6A) as a novel RNA modification at position 37 of tRNAs. Kang BI, Miyauchi K, Matuszewski M, D'Almeida GS, Rubio MAT, Alfonzo JD, Inoue K, Sakaguchi Y, Suzuki T, Sochacka E, Suzuki T; Nucleic Acids Res. 2017;45:2124-2136. PMID:27913733