Extracellular expression of human epidermal growth factor encoded by an Escherichia coli K-12 plasmid stabilized by the ytl2-incR system of Salmonella typhimurium

A plasmid stabilization system, active in high copy-number plasmids, was cloned from the large resident plasmid, pSLT, of Salmonella typhimurium, The ytl2 gene, together with a 249-bp region (termed incR) downstream of the gene, imparted > 10(4)-fold stability to a pBR322-based plasmid, The ytl2-incR region was then used to stabilize a recombinant plasmid carrying the human epidermal growth factor gene (with the Escherichia coli K-12 ompA signal sequence), behind the lacUV5 promoter, In shake flask tests to optimize expression of human epidermal growth factor, loss of recombinant plasmid was