S-adenosyl-L-methionine-dependent guanine N(1)-methyltransferase that catalyzes the formation of N(1)-methylguanine at position 9 (m1G9) in tRNAs. guanosine(9) in tRNA + S-adenosyl-L-methionine = H(+) + N(1)-methylguanosine(9) in tRNA + S-adenosyl-L-homocysteine Belongs to the class IV-like SAM-binding methyltransferase superfamily. TRM10 family.