The function of TYW3 (tRNA-yW synthesizing protein 3 homolog, Ensembl gene identifier ENSG00000162623) is as follows. S-adenosyl-L-methionine-dependent methyltransferase involved in the biosynthesis of wybutosine, a hyper modified guanosine with a tricyclic base located at position 37 of eukaryotic phenylalanine tRNA (tRNA(Phe)) that contributes to maintenance of the translational reading frame. Catalyzes the methylation of 4-demethylwyosine, generating intermediates required for the formation of mature wybutosine. .