Acts as an activator of both rRNA/tRNA and protein methyltransferases (PubMed:20606008, PubMed:26797129). Together with methyltransferase BUD23, methylates the N(7) position of a guanine in 18S rRNA (By similarity). The heterodimer with HEMK2/N6AMT1 catalyzes N5-methylation of ETF1 on 'Gln-185', using S-adenosyl L-methionine as methyl donor (PubMed:20606008, PubMed:26797129). The heterodimer with ALKBH8 catalyzes the methylation of 5-carboxymethyl uridine to 5-methylcarboxymethyl uridine at the wobble position of the anticodon loop in target tRNA species (By similarity). Together with methyltransferase THUMPD3, catalyzes the formation of N(2)-methylguanosine at position 6 in a broad range of tRNA substrates and at position 7 of tRNA(Trp) (By similarity). Involved in the pre-rRNA processing steps leading to small-subunit rRNA production (By similarity). Together with methyltransferase METTL5, specifically methylates the 6th position of adenine in position 1832 of 18S rRNA (By similarity). Heterodimer with BUD23/WBSCR22; this heterodimerization is necessary for the metabolic stability and activity of the catalytic subunit BUD23 (By similarity). Heterodimer with N6AMT1/HEMK2; this heterodimerization is necessary for S-adenosyl-L-methionine-binding to N6AMT1/HEMK2 (PubMed:26797129). Heterodimer with ALKBH8 (By similarity). Heterodimer with METTL5; this heterodimerization is necessary for the stability of the catalytic subunit METTL5 (By similarity). Interacts with THUMPD3; the interaction is direct and is required for THUMPD3 methyltransferase activity (By similarity). Interacts with THUMPD2 (By similarity). Localizes to a polarized perinuclear structure, overlapping partially with the Golgi and lysosomes. Abundantly expressed in the testis, also expressed in the brain, heart, kidney, liver, lung, muscle and spleen. Belongs to the TRM112 family.