This is a family of queuine tRNA-ribosyltransferases EC:2.4.2.29, also known as tRNA-guanine transglycosylase and guanine insertion enzyme. Queuine tRNA-ribosyltransferase modifies tRNAs for asparagine, aspartic acid, histidine and tyrosine with queuine. It catalyses the exchange of guanine-34 at the wobble position with 7-aminomethyl-7-deazaguanine, and the addition of a cyclopentenediol moiety to 7-aminomethyl-7-deazaguanine-34 tRNA; giving a hypermodified base queuine in the wobble position [1,2]. The aligned region contains a zinc binding motif C-x-C-x2-C-x29-H, and important tRNA and 7-aminomethyl-7deazaguanine binding residues [1].

1: Crystal structure of tRNA-guanine transglycosylase: RNA modification by base exchange. Romier C, Reuter K, Suck D, Ficner R; EMBO J 1996;15:2850-2857. PMID:8654383

2: tRNA-guanine transglycosylase from Escherichia coli. Overexpression, purification and quaternary structure. Garcia GA, Koch KA, Chong S; J Mol Biol 1993;231:489-497. PMID:8323579