Production of biologically active N.alpha.-deacetylthymosin .alpha.1 in Escherichia coli through expression of a chemically synthesized gene

Abstract

Thymosin .alpha.1, an immune restorative polypeptide hormone, was synthesized in E. coli by using recombinant DNA cloning techniques. Based on the known amino acid sequence, a gene coding for the thymosin .alpha.1 polypeptide chain was designed and enzymatically assembled from chemically synthesized oligodeoxyribonucleotide fragments. The gene was ligated into plasmid pBR322 and placed under lac operon control and N.alpha.-desacetylthymosin .alpha.1 was expressed as part of a .beta.-galactosidase chimeric protein. Cyanogen bromide cleavage of this protein gave a mixture of polypeptides, among which thymosin .alpha.1 activity was detected by radioimmunoassay (RIA). The E. coli product is identical with native thymosin .alpha.1 isolated from calf thymus in the amino acid sequence but lacks the N-terminal acetyl group. Results of a guinea pig migration inhibition factor (MIF) assay, a terminal deoxyribonucleotidyl transferase (TdT) assay and radioimmunoassay indicate that the N.alpha.-desacetylthymosin .alpha.1 produced by DNA cloning techniques has biological activity equivalent to that of the native hormone.