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Gene Review

trpA  -  tryptophan synthase subunit alpha

Escherichia coli O157:H7 str. EDL933

 
 
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Disease relevance of trpA

  • In this paper, we describe another interesting rRNA mutant, selected as a translational suppressor of the chain-terminating mutant trpA (UGA211) of E. coli [1].
  • The suppressor allows readthrough of UGA mutations at two positions in trpA and at two sites in bacteriophage T4 [2].
 

High impact information on trpA

  • The finding that it suppresses UGA at two positions in trpA and does not suppress the other two termination codons, UAA and UAG, at the same codon positions (or several missense mutations, including UGG, available at one of the two positions) suggests a defect in UGA-specific termination [1].
  • Mutagenesis plasmid vectors were constructed containing three fragments of the trpA gene which together code for about half of the total amino acid residues of the alpha-subunit [3].
  • Thirty-two mutants, contained within the first two trpA fragments (which encompass the first 206 base pairs of the trpA gene and encode the first 63 residues of the alpha-subunit) have been sequenced [3].
  • Selected mutant trpA fragments were subcloned into an overexpression vector in which the trpA gene is controlled by the tac promoter and is inducible by lactose [3].
  • The mutation results in "out-of-phase" translation of the distal portion of the trp mRNA; normal translational termination signal(s) are not encountered and a trpA gene product longer than the wild type protein is produced [4].
 

Biological context of trpA

  • A molecular characterization of spontaneous frameshift mutagenesis within the trpA gene of Escherichia coli [5].
  • There was a dense pattern of reversion sites within the trpA DNA region where reversion events could occur, suggesting that, in general, most DNA sequences are capable of undergoing spontaneous mutational events during replication that can lead to small deletions and insertions [5].
  • These studies also revealed an unpredicted flexibility in the primary amino acid sequence of the trpA product, the alpha subunit of tryptophan synthase [5].
  • The molecular characterization of the mutation that corrected the Eut- phenotype caused by allele Delta903 showed that the new mutation was a deletion of two nucleotides at the tonB-trpA fusion site [6].
  • Five cosmids complementing trpA shared three adjacent HindIII fragments of 2.1, 2.3 and 14 kb [7].
 

Associations of trpA with chemical compounds

  • The nptII (encoding kanamycin resistance) or aacCI (encoding gentamicin resistance) genes were equipped with the tac promoter (Ptac) and the trpA terminator (TtrpA) and then cloned between NotI sites to construct the CAS-Nm (Ptac-nptII-TtrpA) and CAS-Gm (Ptac/PaacCI-aacCI-TtrpA) cassettes [8].
  • The mutagenized fragments were subcloned into the plasmid vector and used to transform to ampicillin resistance (Ampr) a recipient strain containing a UGA mutation in trpA [9].
 

Analytical, diagnostic and therapeutic context of trpA

  • After constructing deltaC1054 by site-directed mutagenesis, we observed, among other differences, that it does not suppress any of the trpA mutations previously reported to be suppressed by the original UGA suppressor [10].

References

  1. UGA suppression by a mutant RNA of the large ribosomal subunit. Jemiolo, D.K., Pagel, F.T., Murgola, E.J. Proc. Natl. Acad. Sci. U.S.A. (1995) [Pubmed]
  2. Mutant 16S ribosomal RNA: a codon-specific translational suppressor. Murgola, E.J., Hijazi, K.A., Göringer, H.U., Dahlberg, A.E. Proc. Natl. Acad. Sci. U.S.A. (1988) [Pubmed]
  3. In vitro mutagenesis and overexpression of the Escherichia coli trpA gene and the partial characterization of the resultant tryptophan synthase mutant alpha-subunits. Milton, D.L., Napier, M.L., Myers, R.M., Hardman, J.K. J. Biol. Chem. (1986) [Pubmed]
  4. Tryptophan operon read-through. Isolation and characterization of an abnormally long tryptophan synthetase alpha subunit from a frame-shift mutant of Escherichia coli. Hardman, J.D., Berger, H., Goodman, M. J. Biol. Chem. (1975) [Pubmed]
  5. A molecular characterization of spontaneous frameshift mutagenesis within the trpA gene of Escherichia coli. Hardin, A., Villalta, C.F., Doan, M., Jabri, M., Chockalingham, V., White, S.J., Fowler, R.G. DNA Repair (Amst.) (2007) [Pubmed]
  6. Molecular characterization of eutF mutants of Salmonella typhimurium LT2 identifies eutF lesions as partial-loss-of-function tonB alleles. Thomas, M.G., O'Toole, G.A., Escalante-Semerena, J.C. J. Bacteriol. (1999) [Pubmed]
  7. Cloning of the trp genes from the archaebacterium Methanococcus voltae: nucleotide sequence of the trpBA genes. Sibold, L., Henriquet, M. Mol. Gen. Genet. (1988) [Pubmed]
  8. Constructs for insertional mutagenesis, transcriptional signal localization and gene regulation studies in root nodule and other bacteria. Reeve, W.G., Tiwari, R.P., Worsley, P.S., Dilworth, M.J., Glenn, A.R., Howieson, J.G. Microbiology (Reading, Engl.) (1999) [Pubmed]
  9. Mutations at three sites in the Escherichia coli 23S ribosomal RNA binding region for protein L11 cause UGA-specific suppression and conditional lethality. Murgola, E.J., Xu, W., Arkov, A.L. Nucleic Acids Symp. Ser. (1995) [Pubmed]
  10. Phenotypic heterogeneity of mutational changes at a conserved nucleotide in 16 S ribosomal RNA. Pagel, F.T., Zhao, S.Q., Hijazi, K.A., Murgola, E.J. J. Mol. Biol. (1997) [Pubmed]
 
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