Abstract: The present invention relates to the recombinant production of amphiphilic peptides with biologically and therapeutically significant activities. In one embodiment, this invention relates to recombinantly producing an amphiphilic peptide by providing a protease-deficient microbial host transformed with an expression vector containing DNA that encodes the amphiphilic peptide under the control of a regulatory sequence operable in the microbial host and expressing the amphiphilic peptide in the transformed microbial host. In another embodiment, this invention relates to providing an E. coli protease-deficient K-12 cell transformed with a vector that expresses a cleavable fusion protein comprising at least part of a carbohydrate binding protein and the amphiphilic peptide in the cell, expressing the fusion protein in the cell, and cleaving the fusion protein to obtain the amphiphilic peptide substantially free of carbohydrate binding protein residues.

Abstract: Positive selection cassettes are disclosed which contain a lethal gene, a promoter, a repressor sequence overlapping the promoter, and a cloning site between the promoter and the lethal gene. Insertion of a foreign nucleic acid sequence into the cloning site prevents expression of the lethal gene. Expression of the lethal gene under nonrepressed conditions kills a host organism containing a positive selection cassette which does not contain the foreign nucleic acid sequence.