Human TRMT2A methylates different components of the translation machinery and contributes to translation fidelity

Methyl-5-uridine (m5U) is one of the most abundant RNA modifications found in cytosolic tRNA. tRNA methyltransferase 2 homolog A (hTRMT2A) is the dedicated mammalian enzyme of m5U conversion at tRNA position 54. However, its RNA binding specificity and functional role in the cell are not well understood. Here we dissected structural and sequence requirements for binding and methylation of its RNA targets. Specificity of tRNA modification by TRMT2A is achieved by a combination of modest binding preference and presence of a uridine in position 54 of tRNAs. Mutational analysis together with crosslinking experiments identified a large hTRMT2A-tRNA binding surface. Furthermore, complementing hTRMT2A interactome studies revealed that TRMT2A interacts with proteins involved in both tRNA and rRNA biogenesis. Consistent with this finding, we observed that TRMT2A not only methylates tRNA, but also rRNA. Finally, we addressed the question of the importance of TRMT2A function by showing that its knockdown reduces translational fidelity. These findings extend the role of hTRMT2A beyond tRNA modification towards rRNA biogenesis and translational fidelity.