High-level expression of 6xHis-tagged proteins in E. coli using pQE vectors is based on the
T5 promoter transcription–translation system. pQE plasmids belong to the pDS family of
plasmids (Bujard et al. 1987) and were derived from plasmids pDS56/RBSII and
pDS781/RBSII-DHFRS (Stüber et al. 1990). These low-copy plasmids (Figure 3) have the
following features: