HIGH-LEVEL EXPRESSION OF HUMAN TRANSFORMING GROWTH FACTOR-ALPHA GENE IN ESCHERICHIA-COLI IN A FUSION GENE SYSTEM WITH HUMAN GROWTH-HORMONE GENE

An artificial gene encoding [Leu14]human growth hormone(hGH), which had a leucine residue at position 14 instead of methionine as in the wild type hGH protein, was constructed and expressed in Escherichia coli at a high level, as well as the [Met14]hGH gene, under the control of the trp promoter including a consensus SD sequence. A human transforming growth factor alpha (TGF-alpha) gene, which had a methionine codon attached to the 5'-terminal region, was chemically synthesized and fused to the [Leu14]hGH gene. The fusion gene was efficiently expressed in E. coli, yielding 48 mg per gram of the wet cell weight. After the fusion protein was cleaved into two parts at the single methionine site by treatment with cyanogen bromide, the desired TGF-alpha was made to form disulfide bonds by a refolding reaction, and then purified by HPLC. The structure of the TGF-alpha was confirmed by amino acid sequence analysis. The biological activity of the purified TGF-alpha was assessed.