S-adenosyl-L-methionine-dependent guanine N(1)-methyltransferase that catalyzes the formation of N(1)-methylguanine at position 9 (m1G9) in tRNAs (PubMed:23042678, PubMed:25053765). Probably not able to catalyze formation of N(1)-methyladenine at position 9 (m1A9) in tRNAs (PubMed:23042678). guanosine(9) in tRNA + S-adenosyl-L-methionine = H(+) + N(1)-methylguanosine(9) in tRNA + S-adenosyl-L-homocysteine Interacts with tRNA. Expressed in embryonic and fetal brain. It is expressed throughout the dorsal telencephalon at 8 and 11 weeks of gestation, with highest expression in ventricular zone and marginal zone. Detected in cerebellar cortex and nuclei, but not in dorsal telencephalon, at later stages. The disease is caused by variants affecting the gene represented in this entry. Belongs to the class IV-like SAM-binding methyltransferase superfamily. TRM10 family.