Certain prokaryotic and eukaryotic tRNAs contain the modified base queuine at position 34. In eubacteria, which produce queuine de novo, the enzyme catalyses the exchange of guanine with the queuine precursor preQ1, which is ultimately modified to queuosine . The enzyme can also use an earlier intermediate, preQ0, to replace guanine in unmodified tRNATyr and tRNAAsn . This enzyme acts after EC 22.214.171.124
, preQ1 synthase, in the queuine-biosynthesis pathway. cf. EC 126.96.36.199
, tRNA-guanosine34 queuine transglycosylase.