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This is a family of queuine tRNA-ribosyltransferases EC:18.104.22.168, also known as tRNA-guanine transglycosylase and guanine insertion enzyme. Queuine tRNA-ribosyltransferase modifies tRNAs for asparagine, aspartic acid, histidine and tyrosine with queuine. It catalyses the exchange of guanine-34 at the wobble position with 7-aminomethyl-7-deazaguanine, and the addition of a cyclopentenediol moiety to 7-aminomethyl-7-deazaguanine-34 tRNA; giving a hypermodified base queuine in the wobble position [1,2]. The aligned region contains a zinc binding motif C-x-C-x2-C-x29-H, and important tRNA and 7-aminomethyl-7deazaguanine binding residues .
Queuine tRNA-ribosyltransferases, also known as tRNA-guanine transglycosylases (TGT) EC, modify tRNAs for asparagine, aspartic acid, histidine and tyrosine with queuine at position 34 and with archaeosine at position 15 in archaeal tRNAs. In bacteria it catalyses the exchange of guanine-34 at the wobble position with 7-aminomethyl-7-deazaguanine (preQ1), and subsequently the addition of a cyclopentenediol moiety to 7-aminomethyl-7-deazaguanine-34 tRNA giving a hypermodified base queuine (Q) in the wobble position [PUBMED:8654383, PUBMED:8323579]. In eukaryotes, TGT catalyzes the irreversible exchange of guanine in the unmodified tRNA with free queuine. Eukaryotes cannot synthesize queuine de novo and must obtain it from the diet or gut flora [PUBMED:11255023].
Romier C, Reuter K, Suck D, Ficner R; , EMBO J 1996;15:2850-2857.: Crystal structure of tRNA-guanine transglycosylase: RNA modification by base exchange. PUBMED:8654383 EPMC:8654383 .
Garcia GA, Koch KA, Chong S; , J Mol Biol 1993;231:489-497.: tRNA-guanine transglycosylase from Escherichia coli. Overexpression, purification and quaternary structure. PUBMED:8323579 EPMC:8323579.