tRNAs contain as many as 13 or 14 nucleotides that are modified posttranscriptionally by enzymes that are highly specific for particular nucleotides in the tRNA structure. TRMT5 methylates the N1 position of guanosine-37 (G37) in selected tRNAs using S-adenosyl methionine (Brule et al., 2004 [PubMed 15248782]).[supplied by OMIM, Mar 2008].