TRNA:m4X modification enzyme (EC 2.1.1.225, TRM13, Trm13p, tRNA:Xm4 modification enzyme) is an enzyme with systematic name S-adenosyl-L-methionine:tRNAPro/His/Gly(GCC) (cytidine/adenosine4-2'-O)-methyltransferase.^[1] This enzyme catalyses the following chemical reaction

(1) S-adenosyl-L-methionine + cytidine⁴ in tRNAPro ${\displaystyle \rightleftharpoons }$ S-adenosyl-L-homocysteine + 2'-O-methylcytidine⁴ in tRNAPro

(2) S-adenosyl-L-methionine + cytidine⁴ in tRNAGly(GCC) ${\displaystyle \rightleftharpoons }$ S-adenosyl-L-homocysteine + 2'-O-methylcytidine⁴ in tRNAGly(GCC)

(3) S-adenosyl-L-methionine + adenosine⁴ in tRNAHis ${\displaystyle \rightleftharpoons }$ S-adenosyl-L-homocysteine + 2'-O-methyladenosine⁴ in tRNAHis

The enzyme from Saccharomyces cerevisiae 2'-O-methylates cytidine⁴ in tRNAPro and tRNAGly(GCC), and adenosine⁴ in tRNAHis.