QIAexpress Type IV Kit

The QIAexpress Type IV Kit from QIAGEN is a reagent kit for the expression and purification of His6-tagged proteins, built around the QIAexpress pQE vector family. These pQE vectors combine the powerful phage T5 promoter — recognized by E. coli RNA polymerase — with a dual lac operator repression module to provide tightly regulated, high-level recombinant protein expression in E. coli. In the presence of high levels of lac repressor, protein synthesis is effectively blocked, which enhances the stability of cytotoxic constructs.

Key vector elements include an optimized promoter/operator consisting of the T5 promoter and two lac operator sequences, a synthetic ribosome binding site (RBSII) for efficient translation, a His tag coding sequence positioned 5' or 3' of a multiple cloning site, and translation stop codons in all reading frames for convenient construct preparation. Two strong transcription terminators — t0 from phage λ and T1 from the E. coli rrnB operon — prevent read-through transcription and help ensure construct stability. The vectors also carry a ColE1 origin of replication derived from pBR322 and a β-lactamase (bla) gene that confers ampicillin resistance. The design allows the His tag to be placed at either the N-terminus or C-terminus of the recombinant protein.

In use, an insert encoding the target protein is cloned into a suitable construct and transformed into an appropriate E. coli strain for expression, with induction triggered by adding IPTG. The QIAexpress Type IV Kit constructs can also be transformed into E. coli for use as shuttle vectors for recombinant protein expression in insect cells, or transfected into mammalian cells. The product belongs to QIAGEN's Secondary Sample Technology portfolio, classified under consumables.