Figure 7.

The Trm10 family of methyltransferases exhibit differences in chemistry and substrate recognition. Trm10 enzymes were originally identified based on their ability to catalyze m¹G₉ methylation (the G₉ target nucleotide is shown in red), which only occurs on a subset of tRNAs in S. cerevisiae (left panel). Subsequent investigation revealed that higher eukaryotes encode up to 3 Trm10 paralogs (TRMT10A, B and C, as indicated) and that the methylation activity and substrate specificities of these enzymes are distinct. TRMT10A (left panel) is most similar to S. cerevisiae Trm10 and exhibits similar biochemical properties. TRMT10B (middle panel), like TRMT10A, is a G₉ methyltransferase but substrate specificity has not been well characterized, while TRMT10C (right panel) is a strictly mitochondrial methyltransferase with much broader tRNA substrate specificity and the unusual ability to catalyze both G₉ and A₉ methylation.