InterPro domain: IPR004803

Queuine is a hypermodified base that occurs in the wobble position of the anticodon of tRNAs Asp, Asn, His and Tyr. Queuine is incorporated into tRNA via a base exchange reaction with guanine catalysed by queuine tRNA-ribosyltransferase (also known as tRNA-guanine transglycosylase). In eukaryotes, queuine is directly exchanged into tRNA while in eubacteria, a queuine precursor (preQ1) is incorporated and ultimately modified to queuine [ 1 , 2 ]. Archaea contain a closely related enzyme ( IPR004804 ) that catalyses a base exchange of guanine for an archaeosine precursor [ 3 ]. This precursor is then subsequently converted to the archaeal-specific modified base archaeosine. Some archaea, such as Archaeoglobus fulgidus, contain both these enzymes.

The eukaryotic tRNA-guanine transglycosylase exists as a heterodimer of a catalytic subunit (QTRT1) and another subunit known as queuine tRNA-ribosyltransferase domain-containing 1 (QTRTD1), whereas the eubacteria enzyme is homodimeric [ 4 , 5 ].

1. Biosynthesis of the 7-deazaguanosine hypermodified nucleosides of transfer RNA. Bioorg. Chem. 31, 24-43
2. Role of aspartate 143 in Escherichia coli tRNA-guanine transglycosylase: alteration of heterocyclic substrate specificity. Biochemistry 45, 617-25
3. Hypermodification of tRNA in Thermophilic archaea. Cloning, overexpression, and characterization of tRNA-guanine transglycosylase from Methanococcus jannaschii. J. Biol. Chem. 275, 28731-8
4. Characterization of cDNA encoding the human tRNA-guanine transglycosylase (TGT) catalytic subunit. Gene 265, 205-12
5. Characterization of the human tRNA-guanine transglycosylase: confirmation of the heterodimeric subunit structure. RNA 16, 958-68