Properties of a human immunoglobulin ε-chain fragment synthesized in Escherichia coli

A fragment of the cloned gene for the human myeloma ND ε chain, coding for the second, third, the fourth domains of the immunoglobulin, has been coupled to the tryptophan control region of an expression plasmid and subcloned in Escherichia coli. Induction of gene expression results in the synthesis of the expected, antigenically active polypeptide of M(r) 40,000, which constitutes 18% of total bacterial protein and yields 55 mg/liter of culture. The immunoglobulin, which is aggregated and packed into large inclusion bodies within the bacterial cell, can be dissolved by denaturing solvents and purified by affinity chromatography using anti-IE Sepharose. Reduced monomeric chains assemble spontaneously into dimers. On assay to measure the inhibition of binding of ¹²⁵I-labeled human E myeloma protein to Fc(ε) receptors on cultured human basophils, the cloned gene product exhibited 20% of the activity of the native protein.