Positive-selection vector with enhanced lytic potential based on a variant of phi X174 phage gene E.

A cloning vector, pUH89, allowing positive selection of recombinant Escherichia coli clones by insertional inactivation of the modified lysis gene E of bacteriophage phi X174, was developed. Ten unique cloning sites were introduced into gene E by site-directed mutagenesis. To achieve efficient expression of the mutagenized gene, the combined lac and tac promoters were used. Additional restriction sites in the flanking sequences allow screening for transcription terminators and the excision of several cartridges suitable for vector construction.