In enzymology, a queuine tRNA-ribosyltransferase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are tRNA-guanine and queuine, whereas its two products are [tRNA]-queuine and guanine.
This enzyme belongs to the family of glycosyltransferases, specifically the pentosyltransferases. The systematic name of this enzyme class is [tRNA]-guanine:queuine tRNA-D-ribosyltransferase. Other names in common use include tRNA-guanine transglycosylase, guanine insertion enzyme, tRNA transglycosylase, Q-insertase, queuine transfer ribonucleate ribosyltransferase, transfer ribonucleate glycosyltransferase, tRNA guanine transglycosidase, guanine, queuine-tRNA transglycosylase, and tRNA-guanine:queuine tRNA-D-ribosyltransferase.
As of late 2007, 36 structures have been solved for this class of enzymes, with PDB accession codes , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , and .