S-adenosyl-L-methionine-dependent guanine N1-methyltransferase that catalyzes the formation of N1-methylguanine at position 9 (m1G9) in tRNAs (PubMed:23042678). Probably not able to catalyze formation of N1-methyladenine at position 9 (m1A9) in tRNAs (PubMed:23042678).