This model is specfic for the tRNA modification enzyme tRNA (guanine-N1)-methyltransferase (trmD). This enzyme methylates guanosime-37 in a number of tRNAs.The enzyme's catalytic activity is as follows: S-adenosyl-L-methionine + tRNA = S-adenosyl-L-homocysteine + tRNA containing N1-methylguanine. [Protein synthesis, tRNA and rRNA base modification]