Hexose-transferase (Htr). Utilizes GDP-mannose, GDP-galactose In tRNAAsp (anticodon QUC) and tRNATyr (anticodon QYA) from certain eukaryotic cells (e.g. mammalian hepatocytes), the nucleoside Q-34 is further hypermodified into a glycosylated derivative by tRNA-queuine glycosyltransferase. This enzymatic activity was detected in rat liver extract and Xenopus leavis oocytes but the protein was not purified.