Tight control of transcription in Toxoplasma gondii using an alternative tet repressor

Int J Parasitol. 2006 Apr;36(4):443-52. doi: 10.1016/j.ijpara.2006.01.005. Epub 2006 Feb 13.


Fusion of yellow fluorescent protein (YFP) to the N-terminus of the Escherichia coli Tn10 tet repressor (TetR) created a functional YFP-TetR repressor with the capacity of 88-fold repression of transcription when expressed in Toxoplasma gondii. As a test promoter we used the T. gondii ribosomal protein RPS13 promoter for which we provide experimental evidence of having a single major transcriptional start site, a condition favourable to the design of inducible expression systems. Integration of four tet operator (tetO) elements, 23-43 bp upstream of the RPS13 transcriptional start site, resulted in maximal repression of transcription (88-fold). Moreover, integration of these four tetO elements reduced the promoter activity only 20% in comparison with the wildtype promoter. Regulation was six-fold higher compared with an inducible expression system employing wildtype TetR. Importantly, only 0.1 microg/ml tetracycline was required for maximal induction demonstrating a higher affinity of tetracycline for YFP-TetR than for wildtype TetR which required 1 microg/ml tetracycline for maximal induction. The use of 0.1 microg/ml tetracycline allows prolonged continuous culturing of T. gondii for which levels of 1 microg/ml tetracycline are toxic. Our results show that YFP-TetR is superior to TetR for transcriptional regulation in T. gondii and we expect that its improved characteristics will be exploitable in other parasites or higher eukaryotes.

MeSH terms

  • Animals
  • Bacterial Proteins / genetics
  • Base Sequence
  • Blotting, Western
  • Dose-Response Relationship, Drug
  • Gene Expression Regulation / drug effects
  • Gene Expression Regulation / genetics
  • Luminescent Proteins / genetics
  • Microscopy, Confocal
  • Molecular Sequence Data
  • Promoter Regions, Genetic / genetics
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Repressor Proteins / genetics*
  • Repressor Proteins / metabolism
  • Tetracyclines / pharmacology
  • Toxoplasma / genetics*
  • Toxoplasma / metabolism
  • Transcription, Genetic*
  • Transfection


  • Bacterial Proteins
  • Luminescent Proteins
  • Recombinant Fusion Proteins
  • Repressor Proteins
  • Tetracyclines
  • tetracycline resistance-encoding transposon repressor protein
  • yellow fluorescent protein, Bacteria