Queuosine Formation in Eukaryotic tRNA Occurs via a Mitochondria-localized Heteromeric Transglycosylase

tRNA guanine transglycosylase (TGT) enzymes are responsible for the formation of queuosine in the anticodon loop (position 34) of tRNAAsp, tRNAAsn, tRNAHis, and tRNATyr; an almost universal event in eubacterial and eukaryotic species. Despite extensive characterization of the eubacterial TGT the eukaryotic activity has remained undefined. Our search of mouse EST and cDNA data bases identified a homologue of the Escherichia coli TGT and three spliced variants of the queuine tRNA guanine transglycosylase domain containing 1 (QTRTD1) gene. QTRTD1 variant_1 (Qv1) was found to be the predominant adult form. Functional cooperativity of TGT and Qv1 was suggested by their coordinate mRNA expression in Northern blots and from their association in vivo by immunoprecipitation. Neither TGT nor Qv1 alone could complement a tgt mutation in E. coli. However, transglycosylase activity could be obtained when the proteins were combined in vitro. Confocal and immunoblot analysis suggest that TGT weakly interacts with the outer mitochondrial membrane possibly through association with Qv1, which was found to be stably associated with the organelle. tRNA guanine transglycosylase (TGT) enzymes are responsible for the formation of queuosine in the anticodon loop (position 34) of tRNAAsp, tRNAAsn, tRNAHis, and tRNATyr; an almost universal event in eubacterial and eukaryotic species. Despite extensive characterization of the eubacterial TGT the eukaryotic activity has remained undefined. Our search of mouse EST and cDNA data bases identified a homologue of the Escherichia coli TGT and three spliced variants of the queuine tRNA guanine transglycosylase domain containing 1 (QTRTD1) gene. QTRTD1 variant_1 (Qv1) was found to be the predominant adult form. Functional cooperativity of TGT and Qv1 was suggested by their coordinate mRNA expression in Northern blots and from their association in vivo by immunoprecipitation. Neither TGT nor Qv1 alone could complement a tgt mutation in E. coli. However, transglycosylase activity could be obtained when the proteins were combined in vitro. Confocal and immunoblot analysis suggest that TGT weakly interacts with the outer mitochondrial membrane possibly through association with Qv1, which was found to be stably associated with the organelle. Queuosine (Q 3The abbreviations used are: QqueuosineTGTtRNA guanine transglycosylaseQv1queuine tRNA guanine transglycosylase domain containing 1 variant 1preQ17-aminomethyl-7-deazaguaninefTGTfull-length mouse TGTtTGTtruncated mouse TGTHAhemagglutininMOPS4-morpholinepropanesulfonic acidDAPI4′,6-diamidino-2-phenylindoleESTexpressed sequence tagGSTglutathione S-transferaseRT-PCRreverse transcription-PCR. 3The abbreviations used are: QqueuosineTGTtRNA guanine transglycosylaseQv1queuine tRNA guanine transglycosylase domain containing 1 variant 1preQ17-aminomethyl-7-deazaguaninefTGTfull-length mouse TGTtTGTtruncated mouse TGTHAhemagglutininMOPS4-morpholinepropanesulfonic acidDAPI4′,6-diamidino-2-phenylindoleESTexpressed sequence tagGSTglutathione S-transferaseRT-PCRreverse transcription-PCR.; (7-{[(4,5-cis-dihydroxy-2-cyclo-penten-1-yl)-amino]methyl}-7-deazaguanosine) is a modified 7-deazaguanosine molecule found at the wobble position of transfer RNA that contains a GUN anticodon sequence: tRNATyr, tRNAAsn, tRNAHis, and tRNAAsp (1.Nishimura S. Prog. Nucleic Acid Res. Mol. Biol. 1983; 28: 49-73Crossref PubMed Scopus (122) Google Scholar). The Q-modification is widely distributed in nature in the tRNA of eubacteria, plants, and animals; a notable exception being yeast and plant leaf cells (2.Kasai H. Oashi Z. Harada F. Nishimura S. Oppenheimer N.J. Crain P.F. Liehr J.G. von Minden D.L. McCloskey J.A. Biochemistry. 1975; 14: 4198-4208Crossref PubMed Scopus (193) Google Scholar, 3.Katze J.R. Basile B. McCloskey J.A. Science. 1982; 216: 55-56Crossref PubMed Scopus (87) Google Scholar). Interestingly, Q-modification has also been detected in aspartyl tRNA from mitochondria of rat (4.Randerath E. Agrawal H.P. Randerath K. Cancer Res. 1984; 44: 1167-1171PubMed Google Scholar) and opossum (5.Mörl M. Dörner M. Pääbo S. Nucleic Acids Res. 1995; 23: 3380-3384Crossref PubMed Scopus (57) Google Scholar). In most eukaryotes, the Q molecule can be further modified by the addition of a mannosyl group to Q-tRNAAsp and a galactosyl group to Q-tRNATyr (1.Nishimura S. Prog. Nucleic Acid Res. Mol. Biol. 1983; 28: 49-73Crossref PubMed Scopus (122) Google Scholar). queuosine tRNA guanine transglycosylase queuine tRNA guanine transglycosylase domain containing 1 variant 1 7-aminomethyl-7-deazaguanine full-length mouse TGT truncated mouse TGT hemagglutinin 4-morpholinepropanesulfonic acid 4′,6-diamidino-2-phenylindole expressed sequence tag glutathione S-transferase reverse transcription-PCR. queuosine tRNA guanine transglycosylase queuine tRNA guanine transglycosylase domain containing 1 variant 1 7-aminomethyl-7-deazaguanine full-length mouse TGT truncated mouse TGT hemagglutinin 4-morpholinepropanesulfonic acid 4′,6-diamidino-2-phenylindole expressed sequence tag glutathione S-transferase reverse transcription-PCR. Eubacteria are unique in their ability to synthesize Q. As part of this biosynthetic process, the eubacterial tRNA guanine transglycosylase (TGT) enzyme inserts the Q precursor molecule, 7-aminomethyl-7-deazaguanine (preQ1) into tRNA, which is then converted to Q by two further enzymatic steps at the tRNA level (6.Iwata-Reuyl D. Bioorg. Chem. 2003; 31: 24-43Crossref PubMed Scopus (107) Google Scholar). Eukaryotes by contrast salvage queuosine from food and enteric bacteria either as the free base (referred to as queuine) or as queuosine 5′-phosphate subsequent to normal tRNA turnover (7.Gündüz U. Katze J.R. J. Biol. Chem. 1984; 259: 1110-1113Abstract Full Text PDF PubMed Google Scholar). A Q-related molecule, archaeosine, is found at position 15 of the D loop of most archaeal tRNA, where it functions to stabilize the tRNA structure (8.Gregson J.M. Crain P.F. Edmonds C.G. Gupta R. Hashizume T. Phillipson D.W. McCloskey J.A. J. Biol. Chem. 1993; 268: 10076-10086Abstract Full Text PDF PubMed Google Scholar). The enzyme involved in archaeosine biosynthesis is structurally and mechanistically related to the eubacterial TGT but with adaptations necessitated by the differences imposed by its unique substrate and tRNA specificity (9.Ishitani R. Nureki O. Fukai S. Kijimoto T. Nameki N. Watanabe M. Kondo H. Sekine M. Okada N. Nishimura S. Yokoyama S. J. Mol. Biol. 2002; 318: 665-677Crossref PubMed Scopus (57) Google Scholar, 10.Stengl B. Reuter K. Klebe G. Chembiochem. 2005; 6: 1926-1939Crossref PubMed Scopus (57) Google Scholar). The crystal structure of the Zymononas mobilis (Z. mobilis) TGT has been determined and revealed the enzyme to be an irregular (β/α)8 TIM barrel with a C-terminal zinc-binding subdomain (11.Romier C. Reuter K. Suck D. Ficner R. EMBO J. 1996; 15: 2850-2857Crossref PubMed Scopus (107) Google Scholar). Insight into the residues involved in catalysis came from mutational and kinetic analysis of the recombinant Escherichia coli enzyme (12.Garcia G.A. Kittendorf J.D. Bioorg. Chem. 2005; 33: 229-251Crossref PubMed Scopus (33) Google Scholar) and from the Z. mobilis TGT structure as an RNA-bound intermediate complexed to the final preQ1-modified RNA product (13.Xie W. Liu X. Huang R.H. Nat. Struct. Biol. 2003; 10: 781-788Crossref PubMed Scopus (95) Google Scholar). This work showed the essential role of Asp-280 (Z. mobilis numbering) as the active site nucleophile. Asp-102, which was originally ascribed the role of active site nucleophile, functions as a general acid/base during catalysis (12.Garcia G.A. Kittendorf J.D. Bioorg. Chem. 2005; 33: 229-251Crossref PubMed Scopus (33) Google Scholar, 10.Stengl B. Reuter K. Klebe G. Chembiochem. 2005; 6: 1926-1939Crossref PubMed Scopus (57) Google Scholar). Although, the E. coli and Z. mobilis TGT enzymes are monomeric in solution (14.Reuter K. Ficner R. J. Bacteriol. 1995; 177: 5284-5288Crossref PubMed Google Scholar), at high protein concentrations the E. coli enzyme can oligomerize (15.Garcia G.A. Koch K.A. Chong S. J. Mol. Biol. 1993; 231: 489-497Crossref PubMed Scopus (32) Google Scholar), and structural data from the Z. mobilis TGT has shown the formation of a 2:1 complex with tRNA; a possible functional requirement for catalysis (10.Stengl B. Reuter K. Klebe G. Chembiochem. 2005; 6: 1926-1939Crossref PubMed Scopus (57) Google Scholar). In contrast to the eubacterial enzyme, which is a single protein species, purification of the eukaryotic TGT suggested that the catalytically active enzyme is a heterodimeric molecule: subunits of 60 and 43 kDa in rabbit erythrocytes (16.Howes N.K. Farkas W.R. J. Biol. Chem. 1978; 253: 9082-9087Abstract Full Text PDF PubMed Google Scholar), 66 and 32 kDa in bovine liver (17.Slany R.K. Müller S.O. Eur. J. Biochem. 1995; 230: 221-228Crossref PubMed Scopus (18) Google Scholar), 60 and 34.5 kDa in rat liver (18.Morris R.C. Brooks B.J. Eriotou P. Kelly D.F. Sagar S. Hart K.L. Elliott M.S. Nucleic Acids Res. 1995; 23: 2492-2498Crossref PubMed Scopus (18) Google Scholar), and a homodimer of two 68-kDa proteins in wheat germ (16.Howes N.K. Farkas W.R. J. Biol. Chem. 1978; 253: 9082-9087Abstract Full Text PDF PubMed Google Scholar, 19.Walden Jr., T.L. Howes N. Farkas W.R. J. Biol. Chem. 1982; 257: 13218-13222Abstract Full Text PDF PubMed Google Scholar). A partial amino acid sequence was recovered from two of these active enzyme preparations. The identity of the proteins from bovine liver (17.Slany R.K. Müller S.O. Eur. J. Biochem. 1995; 230: 221-228Crossref PubMed Scopus (18) Google Scholar) could not be assigned at the time of publication. However, our searches show that the peptides from the are to tRNA and of the to A from rabbit K.L. Farkas W.R. Katze J.R. Biochem. 1996; PubMed Scopus Google Scholar) peptides with to the and a enzyme, is that of the obtained showed to the eubacterial The that in the TGT activity could be in a and Katze K.L. Katze J.R. PubMed Scopus Google Scholar) identified a cDNA a TGT the cDNA into a expression TGT activity in which are to be in tRNA U. Elliott M.S. J.A. Katze J.R. PubMed Scopus Google Scholar). In this for the time the of the eukaryotic tRNA guanine the activity in and the of the active The E. coli TGT was from the and and into the and to the The cDNA for and were from the were for the and site of to search for related proteins by reverse to the of Qv1, mouse TGT and Qv1 were from RNA of a reverse and a QTRTD1 reverse the was converted to an to the for were from a TGT and Qv1 were by the reverse and the and The cDNA was into the and of to the Qv1 was into the and of the to the A truncated of the mouse TGT was also the sequence for the amino This sequence was from the the and The product was into the and of the to of was in the and reverse The Qv1 sequence not been and was in the data base the of expression the TGT and Qv1 cDNA were into the and of and cells tgt was by the of a group were with and and in of protein expression was with in at E. coli and Qv1 proteins were by the was a by of the tag to the to TGT and Qv1 were in and by A to the were further by TGT and Qv1 protein to of TGT and Qv1 to was in at The was with with 1 and with were with a containing 1 tRNA was from E. coli to Scopus Google Scholar). transglycosylase enzyme was to of 1 and of containing of yeast tRNA or E. coli tRNA, and The was for at with of acid and for at to and The was a and at for The was the three The was then with of tRNA was with 1 of 1 was with of A and tRNA with in the wobble position of anticodon loop was as G.A. Biochemistry. 1995; PubMed Scopus Google Scholar). A containing of and of enzyme in was at for were a and at for at The was with of and were to and by RNA was from adult and a QTRTD1 reverse of three variants or an reverse to the for were from a The QTRTD1 variants and the were by the reverse and the and RNA was to and cDNA for TGT and Qv1 from the and As a the membrane was with to the and cells were from the of were in modified with bovine 1 and of in an of at were in in a of to 1 of and mitochondrial were as by the were at 1 in was with for 15 with in with and were with mouse and rabbit and were used at TGT and Qv1 were used at being with were with The were were the and an The E. coli TGT protein was as sequence in protein and searches of the mouse and EST data searches identified a mouse TGT from the queuine tRNA which is to the identified TGT K.L. Katze J.R. PubMed Scopus Google Scholar). the E. coli and mouse TGT proteins as revealed two related mouse of the and and a was identified in mouse by The three proteins from spliced of the queuine tRNA domain containing 1 (QTRTD1) which is of and is from the of In with J.A. J.A. Nucleic Acids Res. PubMed Scopus Google Scholar), the three spliced been assigned the QTRTD1 which is QTRTD1 variant_1 which contains and QTRTD1 which in addition to containing has of a site to with The three QTRTD1 variants were also the S. F. J. Nucleic Acids Res. PubMed Google Scholar), Qv1 was as a and partial Interestingly, in the the of for of In the of a truncated of amino are to be functional and are not of the mouse and Z. mobilis TGT protein revealed a high of amino acid and it is that the eukaryotic TGT a (β/α)8 (13.Xie W. Liu X. Huang R.H. Nat. Struct. Biol. 2003; 10: 781-788Crossref PubMed Scopus (95) Google Scholar). is notable from the that the residues involved in catalysis from the Z. mobilis are the two essential active site residues involved in substrate residues involved in tRNA and residues responsible for the and The three QTRTD1 variants Qv1, and protein of and amino the QTRTD1 variants with the TGT proteins a of mouse TGT and Qv1 sequence identity and The structure of the QTRTD1 variants was the G. 2005; PubMed Scopus Google Scholar), the of which are shown the were to the of the structure with to the Z. mobilis is the of that the QTRTD1 variants a (β/α)8 structure to the TGT the of our the residues to be for catalysis in the TGT proteins are not in the of the QTRTD1 However, is a of residues in the C-terminal subdomain involved in and and a of the active site Asp-280 to a acid A further of the is the almost of residues in the of Qv1 and with an role in formation in the Z. mobilis TGT protein and a of residues in the of mouse TGT (10.Stengl B. Reuter K. Klebe G. Chembiochem. 2005; 6: 1926-1939Crossref PubMed Scopus (57) Google Scholar). The of the QTRTD1 to and The sequence is a acid to to Qv1 and The of this is at However, it is that it contains a which not to the is amino but the is in and and at the of a at the of structure of a T. Gupta R. K. S. PubMed Scopus Google Scholar, U. S. Biol. 2005; 15: Full Text Full Text PDF PubMed Scopus Google Scholar). of amino in and Qv1 is to the TGT proteins This the zinc-binding subdomain and C-terminal to the in Z. mobilis of the (β/α)8 is notable in that it has the sequence its the protein of the of an to a of the zinc-binding The expression of variants is to a or the expression of the QTRTD1 variants in adult were to and which could three of and for Qv1, and was that the Qv1 is in adult mouse and product could be detected for or from the as a the mRNA expression of TGT and Qv1 in mouse by Northern analysis The for proteins was found to in a at for TGT and for Qv1 which with the of and for the TGT and Qv1 cDNA In the of Qv1 a the species, was in with the exception of the analysis revealed a the expression of the TGT and Qv1 data that the of proteins be and by that the proteins in a A search of eukaryotic for the expression of TGT and Qv1 that proteins are found not further their The eukaryotic found not to a Qv1 homologue was the yeast is also the from which the TGT was The that the of TGT and Qv1 in mouse and that the proteins are found in to that for the heterodimeric tRNA guanine transglycosylase activity from protein purification that an or C-terminal or were for TGT and showed that the with either the expression or the of the TGT protein could not be This was not the with the Qv1 the ability of the proteins to or of and of proteins were into and were Our showed that TGT which been by a or the is to A for Qv1 that been the with a and the with an an of was by of the and proteins Confocal of and showed A of the is that the and proteins are from the as by data the that these proteins as suggested by the are the of eukaryotic TGT in E. coli. it has been that the cDNA for the TGT is to E. coli K.L. Katze J.R. PubMed Scopus Google Scholar), and it has been shown that expression of E. coli TGT in a E. coli in of S. C. U. 2002; PubMed Scopus Google Scholar). Despite these a of E. coli that are in Q to the mouse TGT and Qv1 the possible of TGT the protein cells were with used for the expression of E. coli mouse full-length TGT and mouse Qv1 and protein recovered as analysis of the proteins showed that E. coli TGT at kDa the at kDa and Qv1 at kDa that the tag was not from E. coli TGT and Qv1 the tag was from the the enzymes were catalytically the to into tRNA substrate for the eukaryotic enzyme N. Okada N. T. T. Nishimura S. Biochemistry. PubMed Scopus Google and Q-modification to Q is into tRNA it can as a substrate for guanine by the E. coli TGT enzyme N. Nishimura S. J. Biol. Chem. Full Text PDF PubMed Google Scholar). tRNA from cells and cells that were either or the E. coli or Qv1 recombinant proteins As the E. coli TGT guanine into tRNA from the but not tRNA from of recombinant E. coli TGT in the cells in the tRNA being as a substrate for guanine the of the Q-modification in the expression of or Qv1 not Q-modification to tRNA as it remained a substrate for the of The and Qv1 proteins were then in and for tRNA guanine transglycosylase by their ability to guanine into yeast tRNA E. coli TGT as a was that nor Qv1 alone could guanine into However, when in a tRNA guanine transglycosylase activity was which was to that of the E. coli TGT that the of and Qv1 to guanine was not to its being a the ability of the enzymes to their substrate queuine into tRNA was the E. coli TGT enzyme was used to guanine into tRNA and the ability of and Qv1 to the guanine by queuine was nor Qv1 could queuine into However, the two proteins in queuine and of the guanine The of TGT and Qv1 by of to the of the to TGT and Qv1 were in the the recombinant protein to their specificity Confocal analysis of cells showed that the TGT protein has a that is to the for Qv1 The was to from mitochondrial cells were a that Our analysis showed mitochondrial for TGT and Qv1 analysis was and the and mitochondrial of Interestingly, the TGT and Qv1 protein a of which to the of kDa for the recombinant to their the TGT protein was found to be and in was obtained in the mitochondrial The Qv1 by showed a in the mitochondrial a and in the that to the mitochondria an not in our Qv1 is that from the of 1 a acid with the Qv1 of this the a of to the mitochondria P. Eur. J. Biochem. 1996; PubMed Scopus Google Scholar). However, in of EST to an The data to that Qv1 stably with the the TGT protein is that TGT purification of the this the was into cells and the A to that of the was which with the of the TGT protein to with the The of TGT and Qv1 was also by of the in of the of the amino which not part of the (β/α)8 to protein expression The truncated of TGT was found to the transglycosylase activity of was found to be to that of TGT a single to kDa Qv1 at a of kDa that TGT and Qv1 are in The that proteins at a by to could that the proteins a to with the is that of bovine liver tRNA transglycosylase to and 32 kDa (17.Slany R.K. Müller S.O. Eur. J. Biochem. 1995; 230: 221-228Crossref PubMed Scopus (18) Google Scholar). the enzyme activity from rat liver a and and a of enzymatic activity at kDa (18.Morris R.C. Brooks B.J. Eriotou P. Kelly D.F. Sagar S. Hart K.L. Elliott M.S. Nucleic Acids Res. 1995; 23: 2492-2498Crossref PubMed Scopus (18) Google Scholar). the of the TGT and Qv1 proteins to of proteins were and two were at and kDa that TGT and Qv1 not in a in that the TGT with the membrane of the mitochondria and through or with the Qv1 an active tRNA guanine transglycosylase This is the to the eukaryotic complex responsible for Q formation in tRNA as a of TGT and proteins are found in and their are widely distributed in eukaryotic species, in with the of their tRNA (1.Nishimura S. Prog. Nucleic Acid Res. Mol. Biol. 1983; 28: 49-73Crossref PubMed Scopus (122) Google Scholar). The TGT of the eukaryotic enzyme a of residues with to its eubacterial is that it activity in when with either guanine or queuine as However, it be that it is the TGT that the during the sequence of Qv1 from the active eubacterial A of functions for the Qv1 are structure data shown that Z. mobilis TGT in the of a tRNA loop (13.Xie W. Liu X. Huang R.H. Nat. Struct. Biol. 2003; 10: 781-788Crossref PubMed Scopus (95) Google Scholar, 10.Stengl B. Reuter K. Klebe G. Chembiochem. 2005; 6: 1926-1939Crossref PubMed Scopus (57) Google Scholar). The was found to tRNA molecule, as a of imposed by of the was of a with the The was from anticodon with the anticodon where it as a to the tRNA (10.Stengl B. Reuter K. Klebe G. Chembiochem. 2005; 6: 1926-1939Crossref PubMed Scopus (57) Google Scholar). The Qv1 of the eukaryotic complex could be during the A for a also from the eukaryotic requirement to salvage the queuosine 5′-phosphate normal tRNA by of the (7.Gündüz U. Katze J.R. J. Biol. Chem. 1984; 259: 1110-1113Abstract Full Text PDF PubMed Google Scholar). these two are not and could in from the the association of Qv1 with mitochondria a for Q-modification of tRNA be an of the mitochondrial aspartyl tRNA substrate for is at the by which Qv1 to the mitochondria is and further Our data suggest that nor Qv1 with the mitochondria P. Kelly and P. that the protein In a sequence Qv1 as suggested from our of the the of TGT and Qv1 through with to from the Z. mobilis Qv1 an almost of residues to the eubacterial its C-terminal zinc-binding the eukaryotic TGT a of residues in the suggest that Qv1 and TGT these for their Interestingly, the showed recombinant TGT and is possible that substrate could be involved in the two proteins during the as was for the Z. mobilis TGT in the of RNA (10.Stengl B. Reuter K. Klebe G. Chembiochem. 2005; 6: 1926-1939Crossref PubMed Scopus (57) Google Scholar). proteins be as found during protein purification of the tRNA guanine transglycosylase activity (17.Slany R.K. Müller S.O. Eur. J. Biochem. 1995; 230: 221-228Crossref PubMed Scopus (18) Google Scholar, K.L. Farkas W.R. Katze J.R. Biochem. 1996; PubMed Scopus Google Scholar). A further is the of a the rat tRNA guanine transglycosylase activity shown it to be a substrate for and by protein R.C. Brooks B.J. Eriotou P. Kelly D.F. Sagar S. Hart K.L. Elliott M.S. Nucleic Acids Res. 1995; 23: 2492-2498Crossref PubMed Scopus (18) Google Scholar). The that the transglycosylase enzyme as a of of a to be the and a (18.Morris R.C. Brooks B.J. Eriotou P. Kelly D.F. Sagar S. Hart K.L. Elliott M.S. Nucleic Acids Res. 1995; 23: 2492-2498Crossref PubMed Scopus (18) Google Scholar). is a notable in the recombinant TGT and Qv1 and to that of the proteins for this can be at it is possible that sequence for The for the recombinant proteins by kDa for an truncated TGT the amino and kDa for Qv1 that the proteins are with the is that proteins to of kDa been in of rat (18.Morris R.C. Brooks B.J. Eriotou P. Kelly D.F. Sagar S. Hart K.L. Elliott M.S. Nucleic Acids Res. 1995; 23: 2492-2498Crossref PubMed Scopus (18) Google Scholar) and bovine liver (17.Slany R.K. Müller S.O. Eur. J. Biochem. 1995; 230: 221-228Crossref PubMed Scopus (18) Google Scholar) tRNA guanine transglycosylase TGT and Qv1 are found in eukaryotic species, it is to their The of Qv1 from the eubacterial enzymes could that it is the of the at the time when eubacterial and The of the eubacterial and eukaryotic TGT the the eukaryotic enzyme was in most as a of transfer from the Nucleic Acids Res. 2002; PubMed Scopus Google Scholar). The for the eukaryotic TGT to with a for catalysis that the Q-modification of tRNA in the and not in the In with this Q-modification is a in tRNA of the precursor tRNA and of K. J. Mol. Biol. PubMed Scopus Google Scholar). shown that of a yeast not to of Q-modification K. J. Mol. Biol. PubMed Scopus Google Scholar) in to the Q-modification of yeast tRNAAsp when into the E. H. Eur. J. Biochem. PubMed Scopus Google Scholar, P. E. S. G. H. Nucleic Acids Res. 1982; 10: PubMed Scopus Google Scholar). our the of Qv1 from the which be a in the was to the and are not in adult A role of in be from the it was found in an germ the the EST was from a and that it has the zinc-binding it be that it is catalytically The of this the for an analysis of the eukaryotic tRNA guanine transglycosylase and of the role that Q to shown in during Nishimura S. N. Biochem. Res. PubMed Scopus Google Scholar) and N. M. Nishimura S. Eur. J. Biochem. PubMed Scopus Google Scholar, Cancer Res. Google Scholar), and a of during W. G. J.A. G. Cancer Res. Google Scholar), which to the of the G. W. G. 1995; PubMed Scopus Google Scholar). In the of Q has been shown to be in when is from the T. Farkas W.R. Biochem. Res. 230: PubMed Scopus Google Scholar). for this are and for and and for with