Abstract: In this patent application we have described the construction of a novel secretion vector based on E. coli enterotoxin coding sequence. We have shown categorically that pre and pro regions of toxin gene are absolutely necessary for extra cellular secretion of the stable toxin. We have also shown with specific examples that when the nucleotide coding sequence of a heterologous peptide is fused in frame to the end of the pro region in the st gene, the resultant vector in an E. coli host secretes extracellularly correctly processed heterologous peptide. This application also includes construction of suitable vectors where this gene fusion can be achieved. Generally methods to create such fusions involving a) recombinant DNA technology and b) the use of site directed in vitro mutagenesis, have also been described. A general method of purification of heterologous peptides is also described in this application.

Abstract: Disclosed is recombinant plasmid pLS101, consisting essentially of a 2.0 Kb malM gene fragment ligated to a 4.4 Kb T.sub.c r DNA fragment, which is particularly useful for transforming Gram-positive bacteria. This plasmid contains at least four restriction sites suitable for inserting exogeneous gene sequences. Also disclosed is a method for plasmid isolation by penicillin selection, as well as processes for enrichment of recombinant plasmids in Gram-positive bacterial systems.