Production of recombinant porcine tumor necrosis factor alpha in a novel E. coli expression system

DNA sequences encoding porcine tumor necrosis factor alpha (TNF alpha) were reconstructed from a genomic-derived PCR product for expression in Escherichia coli. A synthetic DNA primer containing most of exon III was fused to exon IV sequences by means of PCR. The fused product was then inserted into the novel FLAG vector by restriction and ligation. This initial recombinant construct was propagated in single-strand form through use of a helper phage and subjected to oligonucleotide-directed mutagenesis for the purpose of introducing additional coding sequences from exons II and III. The final construct encoded a fusion protein consisting of the Omp-A signal peptide, a seven-amino acid FLAG peptide and the soluble form of porcine TNF alpha. Bacteria containing this construct produced a protein which was recognized by anti-FLAG monoclonal antibody in Western blots and which was purified by anti-FLAG immunoaffinity chromatography. The purified material was cleaved with enterokinase to remove the FLAG peptide. Both the enterokinase-cleaved form and the uncleaved form were shown to have TNF activity in a WEHI cell cytotoxicity assay.