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Gene Review

tgt  -  tRNA-guanine transglycosylase

Escherichia coli str. K-12 substr. MG1655

Synonyms: ECK0400, JW0396, vacC
 
 
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Disease relevance of tgt

 

High impact information on tgt

  • Isogenic pairs of Escherichia coli, containing or lacking the tRNA-transglycosylase (JE 7335, tgt+ lacZ+ and JE 7337, tgt- lacZ+; JE 7334, tgt+ lacZ- and JE 7336, tgt- lacZ-), have been employed to study the function of queuosine in tRNA [3].
  • Compared with the tgt+ strain (JE 7335), the tgt- mutant (JE 7337) grown under anaerobic conditions, is defective with respect to the nitrate respiration system, in which electrons are transported from D(-)-lactate via quinone and cytochrome bNO3-(556) to nitrate [3].
  • In the case of the anaerobically grown tgt- mutant three proteins are missing in the protein pattern of cytoplasmic membranes [3].
  • The mutant tgt gene was cloned and sequenced; it contained a single point mutation resulting in the change of serine 90 to phenylalanine [4].
  • The smallest of the four possible reading frames, which was still extended at its 5' end compared with the E. coli tgt gene, was overexpressed in E. coli [2].
 

Chemical compound and disease context of tgt

  • Similar phenotypic changes occurred in vacC mutants constructed by insertion of a neomycin resistance gene in shigellae and enteroinvasive E. coli strains, consistent with the hypothesis that the vacC (tgt) gene contributes to the pathogenicity of Shigella flexneri [5].
  • Mutations in the Escherichia coli fnr and tgt genes: control of molybdate reductase activity and the cytochrome d complex by fnr [6].
 

Biological context of tgt

  • The plasmid was subcloned to determine the sequence and organization of the tgt gene [7].
  • The cloned tgt gene from E. coli K-12 restored the virulence phenotype to the vacC mutant of YSH6000 [5].
  • The nucleotide sequence of the 1,822-bp vacC clone was highly (> 98%) homologous to the tgt region of Escherichia coli K-12, which is located at 9.3 min on the linkage map [5].
  • Complementation tests indicated that the vacC function was encoded by an open reading frame expressing a 42.5-kDa protein, which corresponded to the tgt gene of E. coli K-12, coding for tRNA-guanine transglycosylase (Tgt) (K. Reuter, R. Slany, F. Ullrich, and H. Kersten, J. Bacteriol. 173:2256-2264, 1991) [5].
  • The tgt gene of Escherichia coli has been mapped at 9 min on the genome, and mutant pairs containing an intact or mutated tgt allele were obtained after transduction of the tgt locus by P1 bacteriophages into a genetically defined E. coli strain (S. Noguchi, Y. Nishimura, Y. Hirota, and S. Nishimura, J. Biol. Chem. 257:6544-6550, 1982) [6].
 

Associations of tgt with chemical compounds

  • A twofold increase in the frequency of incorrect readthrough of the UAG codon, dependent on the codon context, was observed in the tgt mutant and is suggested to be caused by a tRNA(Tyr) with G in place of queuosine [6].
  • These tgt mutants grew anerobically with fumarate as an electron acceptor, while nitrate or trimethylamine N-oxide could not be reduced [6].
 

Other interactions of tgt

  • The genes are arranged in the following order: ORF 14 (transcribed in the counterclockwise direction), queA, tgt, and ORF 12 (all transcribed in the clockwise direction) [7].
  • The presence of the aroB gene and the putative tgt homologue in unrelated H. pylori strains was confirmed by Southern blot hybridization and by polymerase chain reaction with specific primers [8].
  • Transformation of the original tgt mutants with an fnr gene-containing plasmid reversed the anaerobic defects [6].

References

  1. The promoter of the tgt/sec operon in Escherichia coli is preceded by an upstream activation sequence that contains a high affinity FIS binding site. Slany, R.K., Kersten, H. Nucleic Acids Res. (1992) [Pubmed]
  2. Sequence analysis and overexpression of the Zymomonas mobilis tgt gene encoding tRNA-guanine transglycosylase: purification and biochemical characterization of the enzyme. Reuter, K., Ficner, R. J. Bacteriol. (1995) [Pubmed]
  3. Queuosine modification in tRNA and expression of the nitrate reductase in Escherichia coli. Jänel, G., Michelsen, U., Nishimura, S., Kersten, H. EMBO J. (1984) [Pubmed]
  4. Serine 90 is required for enzymic activity by tRNA-guanine transglycosylase from Escherichia coli. Reuter, K., Chong, S., Ullrich, F., Kersten, H., Garcia, G.A. Biochemistry (1994) [Pubmed]
  5. vacC, a virulence-associated chromosomal locus of Shigella flexneri, is homologous to tgt, a gene encoding tRNA-guanine transglycosylase (Tgt) of Escherichia coli K-12. Durand, J.M., Okada, N., Tobe, T., Watarai, M., Fukuda, I., Suzuki, T., Nakata, N., Komatsu, K., Yoshikawa, M., Sasakawa, C. J. Bacteriol. (1994) [Pubmed]
  6. Mutations in the Escherichia coli fnr and tgt genes: control of molybdate reductase activity and the cytochrome d complex by fnr. Frey, B., Jänel, G., Michelsen, U., Kersten, H. J. Bacteriol. (1989) [Pubmed]
  7. Structure and organization of Escherichia coli genes involved in biosynthesis of the deazaguanine derivative queuine, a nutrient factor for eukaryotes. Reuter, K., Slany, R., Ullrich, F., Kersten, H. J. Bacteriol. (1991) [Pubmed]
  8. Cloning and functional characterization of the genes encoding 3-dehydroquinate synthase (aroB) and tRNA-guanine transglycosylase (tgt) from Helicobacter pylori. Bereswill, S., Fassbinder, F., Völzing, C., Haas, R., Reuter, K., Ficner, R., Kist, M. Med. Microbiol. Immunol. (Berl.) (1997) [Pubmed]
 
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