Escherichia coli (E. coli) bacteria are a powerful tool for the production of heterologous proteins in large quantities, which is of general experimental importance in many fields of natural sciences. E. coli are one of the best-studied organisms and many well-established methodologies used in molecular biology can be applied to modify and handle vectors and coding sequences. Critical parameters for successful production of pPLEX-encoded proteins include the conditions of induction, that is, the time period and temperature of heat shock. As the induction of the αpL promoter usually is mediated by a temperature shift to 42 °, the heat-shock response of E. coli cells, which is accompanied by induced expression of E. coli proteases, can affect the stability of expressed proteins. In addition, the time period of induction determines the accumulation of expression products, which has a crucial effect on yields and the physical form of the expression products. One of the more recent improvements of pPLEX was the insertion of additional restriction sites between the SalI and BclI sites, creating the modified vector pPLEX.