The function of THUMPD3 (THUMP domain 3 tRNA guanosine methyltransferase, Ensembl gene identifier ENSG00000134077) is as follows. Catalytic subunit of the THUMPD3-TRM112 methyltransferase complex, that specifically mediates the S-adenosyl-L-methionine- dependent N(2)-methylation of guanosine nucleotide at position 6 (m2G6) in tRNAs (PubMed:34669960, PubMed:37283053). This is one of the major tRNA (guanine-N(2))-methyltransferases (PubMed:37283053). Also catalyzes the S-adenosyl-L-methionine-dependent N(2)-methylation of guanosine nucleotide at position 7 of tRNA(Trp) (PubMed:34669960). .