In enzymology, a tRNA (guanine-N1-)-methyltransferase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are S-adenosyl methionine and tRNA, whereas its two products are S-adenosylhomocysteine and tRNA containing N1-methylguanine.
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 (guanine-N1-)-methyltransferase. Other names in common use include transfer ribonucleate guanine 1-methyltransferase, tRNA guanine 1-methyltransferase, and S-adenosyl-L-methionine:tRNA (guanine-1-N-)-methyltransferase.
As of late 2007, 6 structures have been solved for this class of enzymes, with PDB accession codes , , , , , and .