The E. coli expression system to overproduce a harmful protein, carboxypeptidase Taq was developed. Since expression plasmid pCK305N containing the colicin promoter already has the initiation codon on the restriction site, the initiation codon of the CPase Taq gene was removed. Expression plasmid pCP4-col includes the entire CPase Taq gene, which is directed by the colicin promoter. E. coli cells harboring pCP-col produced a high amount of the enzyme when they were cultured in the present of mitomycin C (0.4 ${mu}g$/ml). An amount of purified enzyme produced by pCP4-col directed by the colicin promoter was 10.5 mg. This result indicated that the novel E. coli expression system controlled by the colicin promoter could produce almost twice amounts of CPase Taq than the conventional system controlled by the tart promoter.