Features of expression vectors. All vectors except PSAP1 (backbone is pQE80L, Qiagen, Hilden, Germany) and PSKn1 (backbone is pET28c, Novagen, San Diego, CA, USA) are derived from pET47b (Novagen). Start and Stop primers are used to linearize the vectors for insertion of target sequence by co-transformation. The overlaps with the target PCR are indicated. The sequences of the vector template plasmids are available on request. The nomenclature permits fast recognition of the features of the vectors: The names start with PS for positive selection with chloramphenicol (Cm80 = Chloramphenicol 80 mg/L), ampicillin (Amp) or kanamycin (Kan) and NS, for negative selection with ccdB, respectively. The proteolytic cleavage site is indicated by T for thrombin and P for prescission proteases. The tag(s) are indicated and finally the antibiotic resistance is given followed by a number. The concentration of the antibiotics can vary greatly depending on the vector's copy number per cell.