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Gene Review

toxA  -  exotoxin A

Pseudomonas aeruginosa PAO1

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Disease relevance of toxA

  • The exotoxin A gene (toxA) from Pseudomonas aeruginosa PAO1 was expressed from the lac promoter in Escherichia coli, and the localization of the toxin A protein was determined [1].
  • The transcription of regA, a positive regulator of toxA, was also found to be inhibited by multiple copies of the E. coli fur gene [2].

High impact information on toxA

  • Mutations in the UCBPP-PA14 toxA, plcS, and gacA genes resulted in a significant reduction in pathogenicity in both hosts, indicating that these genes encode virulence factors required for the full expression of pathogenicity in both plants and animals [3].
  • We previously described P. aeruginosa PtxR as a transcriptional activator of the exotoxin A gene toxA [4].
  • In this report, we describe the isolation of a new toxA regulatory gene (ptxR) which affects exotoxin A production in P. aeruginosa [5].
  • Neither toxA nor regAB mRNA was detectable in a delta pvdS mutant [6].
  • First, we constructed a strain with the regAB locus deleted from the chromosome, PA103 delta regAB::Gm. toxA transcription was obliterated in strain PA103 delta regAB::Gm, demonstrating that the regAB locus is essential for ETA production [7].

Biological context of toxA

  • The ETA structural gene, toxA, is regulated at the transcriptional level by the gene products of the regAB operon [6].
  • The toxA promoter-beta-galactosidase fusion plasmid could not be maintained in PA103-8. beta-Galactosidase expression driven by the toxA promoter was absent in the mutant PA103-19 and occurred at a low level, which was not repressed by iron in mutants PA103-15 and PA103-16 [8].
  • Complementation of PA103-29 with both regA and regB resulted in a high level of transcription from the P1 promoter and a corresponding early transcriptional activation of toxA [9].
  • Nucleotide sequence and Southern hybridization data revealed a mosaic genome organization in a region that extends several thousand base pairs upstream of the exotoxin A (toxA) gene in Pseudomonas aeruginosa [10].
  • The insertions occurred in the same location upstream of the toxA gene, suggesting that this type of genetic recombination may also be associated with mucoid conversion in some P. aeruginosa clinical isolates [11].

Anatomical context of toxA

  • DNA probes specific for P. aeruginosa elastase (lasB) and exotoxin A (toxA) were used to examine the population transcript accumulation of 21 sputum samples taken from 10 patients [12].

Associations of toxA with chemical compounds

  • RNase protection analysis of toxA and regAB transcription in PAO1, PAO6261 and the C6 mutant corroborated the results of quantitative dot-blot assays of ETA [13].
  • Thus, pvdS (but not toxA) appears to be required for optimal virulence of P. aeruginosa, particularly in tissues preferentially exposed to high O2 tensions (e.g., aortic vegetations) [14].
  • In contrast, citrate and isocitrate diminished toxA transcription [15].
  • Glutamate had no effect on toxA (ETA-encoding) transcription, which implies that glutamate primarily increases the number of toxin-producing cells [15].

Regulatory relationships of toxA

  • This result suggested that toxA was regulated independently of algD [16].
  • The transcription of the ETA structural gene (toxA) has been shown to be positively regulated by the product of the toxR gene (also called regA) [17].

Other interactions of toxA

  • Footprinting analysis revealed Vfr protected sequences upstream of toxA, regA, and the quorum sensing regulator lasR, that are similar to but significantly divergent from the CRP consensus binding sequence, and Vfr causes similar DNA bending to CRP in bound target sequences [18].
  • Transcriptional analysis of the Pseudomonas aeruginosa toxA regulatory gene ptxR [19].
  • Experiments using a toxA specific probe have revealed the the toxR gene product appears to regulate the expression of ETA at the transcriptional level [20].
  • Few fragment length classes were seen for the alg60-, algR- and toxA-encoding SpeI fragments [21].
  • When a Spearman rank correlation analysis was done on the samples, we found no correlation between algD transcript accumulation and toxA transcript accumulation [16].

Analytical, diagnostic and therapeutic context of toxA

  • The methods, representing powerful tools for hospital molecular epidemiology, included hybridization of restricted chromosomal DNA with toxA and genes coding for rRNA (rDNA) used as probes and macrorestriction analysis of SpeI-digested DNA by pulsed-field gel electrophoresis [22].
  • Comparison of the results of MLST with those of toxA typing and serotyping revealed that strains with identical STs may possess different toxA types and diverse serotypes [23].
  • The cellular location of the toxA subclone products in P. aeruginosa was determined by immunoblotting analysis [24].
  • Real-time PCR transcriptional analysis showed that the copy number of toxA mRNA in PA103-2R is significantly higher than in PA103 in both the presence and absence of iron, yet no similar increase in either regAB or ptxR mRNA copy number was detected [25].
  • This was done using Northern blot hybridization experiments (with toxA, regA, and ptxR probes), and ptxR transcriptional fusion studies [26].


  1. Secretion of toxin A from Pseudomonas aeruginosa PAO1, PAK, and PA103 by Escherichia coli. Hamood, A.N., Wick, M.J., Iglewski, B.H. Infect. Immun. (1990) [Pubmed]
  2. Regulation of toxA and regA by the Escherichia coli fur gene and identification of a Fur homologue in Pseudomonas aeruginosa PA103 and PA01. Prince, R.W., Storey, D.G., Vasil, A.I., Vasil, M.L. Mol. Microbiol. (1991) [Pubmed]
  3. Common virulence factors for bacterial pathogenicity in plants and animals. Rahme, L.G., Stevens, E.J., Wolfort, S.F., Shao, J., Tompkins, R.G., Ausubel, F.M. Science (1995) [Pubmed]
  4. PtxR modulates the expression of QS-controlled virulence factors in the Pseudomonas aeruginosa strain PAO1. Carty, N.L., Layland, N., Colmer-Hamood, J.A., Calfee, M.W., Pesci, E.C., Hamood, A.N. Mol. Microbiol. (2006) [Pubmed]
  5. Isolation and characterization of a Pseudomonas aeruginosa gene, ptxR, which positively regulates exotoxin A production. Hamood, A.N., Colmer, J.A., Ochsner, U.A., Vasil, M.L. Mol. Microbiol. (1996) [Pubmed]
  6. Exotoxin A production in Pseudomonas aeruginosa requires the iron-regulated pvdS gene encoding an alternative sigma factor. Ochsner, U.A., Johnson, Z., Lamont, I.L., Cunliffe, H.E., Vasil, M.L. Mol. Microbiol. (1996) [Pubmed]
  7. Linker insertion scanning of regA, an activator of exotoxin A production in Pseudomonas aeruginosa. Raivio, T.L., Hoffer, D., Prince, R.W., Vasil, M.L., Storey, D.G. Mol. Microbiol. (1996) [Pubmed]
  8. Characterization of Pseudomonas aeruginosa mutants that are deficient in exotoxin A synthesis and are altered in expression of regA, a positive regulator of exotoxin A. West, S.E., Kaye, S.A., Hamood, A.N., Iglewski, B.H. Infect. Immun. (1994) [Pubmed]
  9. Effect of regB on expression from the P1 and P2 promoters of the Pseudomonas aeruginosa regAB operon. Storey, D.G., Raivio, T.L., Frank, D.W., Wick, M.J., Kaye, S., Iglewski, B.H. J. Bacteriol. (1991) [Pubmed]
  10. Possible insertion sequences in a mosaic genome organization upstream of the exotoxin A gene in Pseudomonas aeruginosa. Pritchard, A.E., Vasil, M.L. J. Bacteriol. (1990) [Pubmed]
  11. Genetic rearrangement associated with in vivo mucoid conversion of Pseudomonas aeruginosa PAO is due to insertion elements. Sokol, P.A., Luan, M.Z., Storey, D.G., Thirukkumaran, P. J. Bacteriol. (1994) [Pubmed]
  12. Population transcript accumulation of Pseudomonas aeruginosa exotoxin A and elastase in sputa from patients with cystic fibrosis. Storey, D.G., Ujack, E.E., Rabin, H.R. Infect. Immun. (1992) [Pubmed]
  13. Ferric uptake regulator mutants of Pseudomonas aeruginosa with distinct alterations in the iron-dependent repression of exotoxin A and siderophores in aerobic and microaerobic environments. Barton, H.A., Johnson, Z., Cox, C.D., Vasil, A.I., Vasil, M.L. Mol. Microbiol. (1996) [Pubmed]
  14. The oxygen- and iron-dependent sigma factor pvdS of Pseudomonas aeruginosa is an important virulence factor in experimental infective endocarditis. Xiong, Y.Q., Vasil, M.L., Johnson, Z., Ochsner, U.A., Bayer, A.S. J. Infect. Dis. (2000) [Pubmed]
  15. Physiological characterization of Pseudomonas aeruginosa during exotoxin A synthesis: glutamate, iron limitation, and aconitase activity. Somerville, G., Mikoryak, C.A., Reitzer, L. J. Bacteriol. (1999) [Pubmed]
  16. Positive correlation of algD transcription to lasB and lasA transcription by populations of Pseudomonas aeruginosa in the lungs of patients with cystic fibrosis. Storey, D.G., Ujack, E.E., Mitchell, I., Rabin, H.R. Infect. Immun. (1997) [Pubmed]
  17. ToxR (RegA)-mediated in vitro transcription of Pseudomonas aeruginosa toxA. Walker, S.L., Hiremath, L.S., Wozniak, D.J., Galloway, D.R. Gene (1994) [Pubmed]
  18. Characterization of DNA-binding specificity and analysis of binding sites of the Pseudomonas aeruginosa global regulator, Vfr, a homologue of the Escherichia coli cAMP receptor protein. Kanack, K.J., Runyen-Janecky, L.J., Ferrell, E.P., Suh, S.J., West, S.E. Microbiology (Reading, Engl.) (2006) [Pubmed]
  19. Transcriptional analysis of the Pseudomonas aeruginosa toxA regulatory gene ptxR. Colmer-Hamood, J.A., Aramaki, H., Gaines, J.M., Hamood, A.N. Can. J. Microbiol. (2006) [Pubmed]
  20. Nucleotide sequence and characterization of toxR: a gene involved in exotoxin A regulation in Pseudomonas aeruginosa. Wozniak, D.J., Cram, D.C., Daniels, C.J., Galloway, D.R. Nucleic Acids Res. (1987) [Pubmed]
  21. Gradient of genomic diversity in the Pseudomonas aeruginosa chromosome. Römling, U., Greipel, J., Tümmler, B. Mol. Microbiol. (1995) [Pubmed]
  22. Discriminatory power of three DNA-based typing techniques for Pseudomonas aeruginosa. Grundmann, H., Schneider, C., Hartung, D., Daschner, F.D., Pitt, T.L. J. Clin. Microbiol. (1995) [Pubmed]
  23. Development of a multilocus sequence typing scheme for the opportunistic pathogen Pseudomonas aeruginosa. Curran, B., Jonas, D., Grundmann, H., Pitt, T., Dowson, C.G. J. Clin. Microbiol. (2004) [Pubmed]
  24. Toxin A secretion in Pseudomonas aeruginosa: the role of the first 30 amino acids of the mature toxin. McVay, C.S., Hamood, A.N. Mol. Gen. Genet. (1995) [Pubmed]
  25. Regulation of toxA by PtxR in Pseudomonas aeruginosa PA103. Carty, N.L., Rumbaugh, K.P., Hamood, A.N. Can. J. Microbiol. (2003) [Pubmed]
  26. Expression of ptxR and its effect on toxA and regA expression during the growth cycle of Pseudomonas aeruginosa strain PAO1. Colmer, J.A., Hamood, A.N. Can. J. Microbiol. (1999) [Pubmed]
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