The reaction occurs in the reverse direction. This enzyme catalyses one of the early steps in the synthesis of queuosine (Q-tRNA), and is followed by the action of EC
2.4.2.29, tRNA-guanosine34 transglycosylase. Queuosine is found in the wobble position of tRNAGUN in Eukarya and Bacteria [2] and is thought to be involved in translational modulation. The enzyme is not a GTP cyclohydrolase, as was thought previously based on sequence-homology studies.