In enzymology, a tRNA (5-methylaminomethyl-2-thiouridylate)-methyltransferase (EC 2.1.1.61) is an enzyme that catalyzes the chemical reaction

S-adenosyl-L-methionine + tRNA ${\displaystyle \rightleftharpoons }$ S-adenosyl-L-homocysteine + tRNA containing 5-methylaminomethyl-2-thiouridylate

Thus, the two substrates of this enzyme are S-adenosyl methionine and tRNA, whereas its two products are S-adenosylhomocysteine and tRNA containing 5-methylaminomethyl-2-thiouridylic acid.

This enzyme belongs to the family of transferases, specifically those transferring one-carbon group methyltransferases. The systematic name of this enzyme class is S-adenosyl-L-methionine:tRNA (5-methylaminomethyl-2-thio-uridylate)-methyltransferase. Other names in common use include transfer ribonucleate 5-methylaminomethyl-2-thiouridylate, 5-methyltransferase, and tRNA 5-methylaminomethyl-2-thiouridylate 5'-methyltransferase.

As of late 2007, 4 structures have been solved for this class of enzymes, with PDB accession codes 2DER, 2DET, 2DEU, and 2HMA.

• Taya Y, Nishimura S (1973). "Biosynthesis of 5-methylaminomethyl-2-thiouridylate. I. Isolation of a new tRNA-methylase specific for 5-methylaminomethyl-2-thiouridylate". Biochem. Biophys. Res. Commun. 51 (4): 1062–8. doi:10.1016/0006-291X(73)90035-1. PMID 4703553.
• Taya Y, Nishimura S (1977). Salvatore, F., Borek, E., Zappia, V., Williams-Ashman, H.G., Schlenk, F. (eds.). "The Biochemistry of Adenosylmethionine". New York: Columbia University Press: 251. {{cite journal}}: Cite journal requires |journal= (help)