The Enzyme Database

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Accepted name: tRNA-guanosine34 transglycosylase
Reaction: (1) guanine34 in tRNA + queuine = queuine34 in tRNA + guanine
(2) guanine34 in tRNA + 7-aminomethyl-7-carbaguanine = 7-aminomethyl-7-carbaguanine34 in tRNA + guanine
For diagram of queuine biosynthesis, click here
Glossary: 7-aminomethyl-7-carbaguanine = preQ1 = 7-aminomethyl-7-deazaguanine
7-cyano-7-carbaguanine = preQ0 = 7-cyano-7-deazaguanine
queuine = base Q = 2-amino-5-({[(1S,4S,5R)-4,5-dihydroxycyclopent-2-en-1-yl]amino}methyl)-1,7-dihydropyrrolo[3,2-e]pyrimidin-4-one
Other name(s): guanine insertion enzyme (ambiguous); tRNA transglycosylase (ambiguous); Q-insertase (ambiguous); queuine34 transfer ribonucleate ribosyltransferase; transfer ribonucleate glycosyltransferase (ambiguous); tRNA guanine34 transglycosidase; queuine tRNA-ribosyltransferase (ambiguous); TGT; [tRNA]-guanine34:queuine tRNA-D-ribosyltransferase; transfer ribonucleic acid guanine34 transglycosylase
Systematic name: tRNA-guanosine34:queuine tRNA-D-ribosyltransferase
Comments: Certain prokaryotic and eukaryotic tRNAs contain the modified base queuine at position 34. In eukaryotes queuine is salvaged from food and incorporated into tRNA directly via a base-exchange reaction, replacing guanine. 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 [4,5]. The eubacterial enzyme can also use an earlier intermediate, preQ0, to replace guanine in unmodified tRNATyr and tRNAAsn [2]. This enzyme acts after EC, preQ1 synthase, in the queuine-biosynthesis pathway.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number: 72162-89-1
1.  Howes, N.K. and Farkas, W.R. Studies with a homogeneous enzyme from rabbit erythrocytes catalyzing the insertion of guanine into tRNA. J. Biol. Chem. 253 (1978) 9082–9087. [PMID: 721832]
2.  Okada, N., Noguchi, S., Kasai, H., Shindo-Okada, N., Ohgi, T., Goto, T. and Nishimura, S. Novel mechanism of post-transcriptional modification of tRNA. Insertion of bases of Q precursors into tRNA by a specific tRNA transglycosylase reaction. J. Biol. Chem. 254 (1979) 3067–3073. [PMID: 372186]
3.  Shindo-Okada, N., Okada, N., Ohgi, T., Goto, T. and Nishimura, S. Transfer ribonucleic acid guanine transglycosylase isolated from rat liver. Biochemistry 19 (1980) 395–400. [PMID: 6986171]
4.  Todorov, K.A. and Garcia, G.A. Role of aspartate 143 in Escherichia coli tRNA-guanine transglycosylase: alteration of heterocyclic substrate specificity. Biochemistry 45 (2006) 617–625. [DOI] [PMID: 16401090]
5.  Boland, C., Hayes, P., Santa-Maria, I., Nishimura, S. and Kelly, V.P. Queuosine formation in eukaryotic tRNA occurs via a mitochondria-localized heteromeric transglycosylase. J. Biol. Chem. 284 (2009) 18218–18227. [DOI] [PMID: 19414587]
[EC created 1984, modified 2007, modified 2012]

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