pQE-TriSystem Vector

For parallel expression of His-tagged proteins in E. coli, mammalian cells, and baculovirus-infected insect cells using a single construct


  • No need for time-consuming subcloning procedures
  • Obtain post-translational modifications in insect or mammalian cells
  • One construct provides efficient expression in three expression systems
pQE-TriSystem Vector

Cat. No. / ID: 33903

25 μg pQE-TriSystem Vector DNA
The pQE-TriSystem Vector is intended for molecular biology applications. This product is not intended for the diagnosis, prevention, or treatment of a disease.

Product Details

The pQE TriSystem Vector allows for high-level expression of His-tagged proteins from a single vector containing three different expression systems. There is the T5 promoter/lac operator transcription–translation system for expression in E. coli, the p10 promoter for baculovirus-based expression in insect cells, and the CAG (CMV/actin/globin) promoter for expression in mammalian cells.


The pQE-TriSystem vector contains CAG, T5, and p10 promoters that enable 6xHis-tagged protein expression in mammalian, E. coli, and baculovirus-infected insect cells, respectively (see figure  pQE TriSystem). Preliminary studies can be carried out in bacterial expression systems, using the strong T5 promoter, which is recognized by E. coli polymerase, and allows efficient expression of proteins in any E. coli strain. If expression in mammalian or insect cells is required — to obtain post-translational modifications, for example — the same construct can be used without the need for time-consuming subcloning procedures.
See figures


QIAexpress pQE vectors combine a powerful phage T5 promoter (recognized by E. coli RNA polymerase) with a double lac operator repression module to provide tightly regulated, high-level expression of recombinant proteins in E. coli. Protein synthesis is effectively blocked in the presence of high levels of lac repressor and the stability of cytotoxic constructs is enhanced. The pQE vectors (see table and figure  pQE Vectors) enable placement of the 6xHis tag at either the N- or C-terminus of the recombinant protein.

Elements present in QIAexpress pQE Vectors
1. Optimized promoter/operator elementConsists of the phage T5 promoter and two lac operator sequences, which increase the probability of lac repressor binding and ensure efficient repression of the powerful T5 promoter
2. Synthetic ribosomal binding site RBSIIFor efficient translation
3. His-tag coding sequenceEither 5' or 3' to the polylinker cloning region
4. Translational stop codonsIn all reading frames for convenient preparation of expression constructs
5. Two strong transcriptional terminatorst0 from phage lambda, and T1 from the rrnB operon of E. coli, to prevent read-through transcription and ensure stability of the expression construct

6. ColE1 origin of replicatio

From pBR322
7. beta-lactamase gene (bla)Confers ampicillin resistance
See figures


Inserts encoding proteins of interest are cloned into appropriate constructs and transformed into a suitable E. coli strain for expression. Expression is induced by addition of IPTG. Vector pQE-TriSystem constructs can be transformed into E. coli, used as a shuttle vector for recombinant protein expression in insect cells, or transfected into mammalian cells.


The QIAexpress Expression System provides high-level expression of proteins suitable for
many applications, including:

  • Purification of functional, conformationally active proteins
  • Purification under denaturing conditions for antibody production
  • Crystallization for determination of three-dimensional structure
  • Assays involving protein-protein and protein-DNA interactions

Supporting data and figures


expressionIn vivo
expressionspeciesE.coli, mammalian & insect cells
tag6xHis tag
norcterminaltagC-terminal tag


Selection Guides (1)
Kit Handbooks (1)
A handbook for high-level expression and purification of 6xHis-tagged proteins


Is it possible to use QIAGEN's pQE-TriSystem Vectors with the EasyXpress Protein Synthesis Insect Kit?

No, the pQE-TriSystem vectors contain a T5 Promoter. The expression plasmid used with the EasyXpress Protein Synthesis Insect Kit must contain a T7 Promoter.

FAQ ID -876
How can I increase expression of my 6xHis-tagged protein in E. coli?

Low-level expression can occur because the protein is toxic or unstable, or because the expression construct is not maintained in the cells during growth. In some cases, the 5' end of the inserted DNA sequence may encode elements that interfere with transcription or translation (e.g., masking of the Shine-Dalgarno sequence by stem-loop structures resulting from inverted repeats). In these instances, the sequence being expressed should be checked and modified if necessary. Modifications of growth media and different host strains may also have an effect on expression.

Please review the section "Specific considerations" in the Chapter 'Expression in E. coli' of the QIAexpressionist Handbook and refer to standard literature in protein science (e.g., Current Protocols in Protein Science, eds. John Wiley and Sons, New York) for additional information.

FAQ ID -63
How can I increase the amount of soluble recombinant protein in E. coli expression?

The QIAexpress Protein Purification System allows easy solubilization of 6xHis-tagged proteins sequestered into insoluble inclusion bodies by using denaturants such as 6 M Guanidine-HCl or 8 M Urea, or a variety of detergents. Proteins purified under denaturing conditions can then be refolded if necessary before use (please see: Wingfield, P. T., Palmer, I., and Liang, S.-M. (1995). Folding and purification of insoluble (inclusion-body) proteins from Escherichia coli. In: Current Protocols in Protein Science, vol. 1, Coligan, J. E., Dunn, B. M., Ploegh, H. L., Speicher, D. W., and Wingfield, P.T. eds. Wiley and Sons, Inc. New York, pp. 6.5.1–6.5.27.). The QIAexpressionist also contains recommendations for refolding proteins prior to the Appendix section of the handbook.

To increase levels of soluble protein, here are a few recommendations:

  • a reduction in growth temperature following induction may be helpful. Growth temperature often directly affects both expression levels and protein solubility, and lower temperatures will reduce expression levels leading to a higher amount of soluble protein.
  • the culture can be grown to a higher cell density before induction and the expression period can be kept to a minimum.
  • The IPTG concentration can be reduced from 1 mM to 0.005 mM, which would reduce the expression level by 90–95%.
  • it may be sufficient to change the host strain used, since certain strains tolerate some proteins better than others and allow higher levels of expression before forming inclusion bodies.
  • many proteins require metal cofactors in order to remain soluble, and the addition of metal salts to the culture media may be helpful. If the metal requirements of the protein are not known, a number of different supplements should be tested. Note that some divalent cations may interfere with protein binding to Ni-NTA.



FAQ ID -64
What is the origin of replication and the plasmid copy number of the pQE vectors?
The QIAexpress pQE vectors contain a pBR322 derived ColE1 origin of replication and are classified as low-copy plasmids (by our estimate, approximately 20-30 copies per cell; exact numbers have not been determined). The pQE-TriSystem Vector has a pUC origin of replication and is classified as a high-copy vector. Please see also FAQ 350 for general information on replication origins and copy numbers of various commonly used plasmids.
FAQ ID -338
How should I propagate pQE expression plasmids?

QIAexpress pQE vectors and constructs can be maintained in any E. coli strain that is ampicillin-sensitive and carries the pREP4 repressor plasmid, or harbors the lacIq gene on the F-factor episome.

M15 and SG13009 E. coli host strains carry lacI on the plasmid pREP4, while XL1-Blue or the JM series contain an episomal copy of lacIq.

LacIq is a mutation of lacI that produces very high levels of the lac repressor. Initial cloning and propagation using XL1-Blue is recommended because plasmid preparations derived from QIAexpress host strains will also contain pREP4 DNA, which could make clone analysis more difficult.

Alternatively, the pQE-80L series of expression vectors which encodes a lacIq repression module, allows use of any E. coli host strain.

FAQ ID -58
Do pQE vectors contain the CAT gene?
The chloramphenicol acetyl transferase gene (CAT) present between t0 and T1 has no promoter and is not normally expressed. Depending on the bacterial strain and insert,low CAT activities may be detectable
FAQ ID -362
How can I be sure that I am harvesting my induced bacterial culture at the best time point for protein expression?

To optimize the expression of a given recombinant protein, a time-course analysis of the level of protein expression in the induced culture is recommended. Intracellular protein content is often a balance between the amount of soluble protein in the cells, the formation of inclusion bodies, and protein degradation. By checking the 6xHis-tagged protein present at various times after induction in the soluble and insoluble fractions, the optimal induction period can be established, and the bacterial culture can be harvested at this time. It may be useful to perform plasmid Mini preparations on culture samples during the time-course to enable monitoring of plasmid (expression construct) maintenance.

Below, you can see an example of a time course of recombinant protein expression using the QIAexpress System. You can find this information also in the Section 'Expression in E. coli' in the QIAexpressionist Handbook. The handbook is an important resource for useful background information and protocols. For instructions on how to isolate protein from the soluble and insoluble fractions of induced cultures please see Protocol 14. "Protein minipreps of 6x His-tagged proteins from E. coli under native conditions" and Protocol 19. "6xHis-tagged protein minipreps under denaturing conditions."




Time course of expression using the QIAexpress System. Expression of 6xHis-tagged DHFR was induced with 1 mM IPTG. Aliquots were removed at the times indicated and purified on Ni-NTA Agarose under denaturing conditions. Proteins were visualized by Coomassie staining. Yields per liter culture were 2.8, 5.5,12.3, 33.8, and 53.9 mg, respectively. ■A Crude cell lysate; ■B purification with Ni-NTA. 1: flow-through, 2 & 3: first and second eluates; M: markers; C: noninduced control.



FAQ ID -788