A bifunctional vector system for controlled expression and subsequent release of the cloned gene product by phi X174 lysis protein-E.

A new bifunctional Escherichia coli cloning vector, pSB50, is presented. The plasmid allows controlled expression of a gene of interest under control of the lac promoter and the subsequent release of the cloned product by the use of bacteriophage phi X174 lysis protein-E, the gene of which is under control of the phage Lambda pL promoter. To ensure optimal repression of the Lambda pL promoter and the lac promoter in plasmid pSB50, E. coli strain UB89-1 was constructed which carries a chromosomal copy of the lambda cl857 repressor allele and the laclq1 allele, respectively. Here, we employ the E-based lysis system to release human prourokinase to the culture medium.