Expression of human IgE-binding factor (sCD23) in Escherichia coli

Previously, we cloned cDNA coding for type II Fc receptor for human IgE (CD23 or FcERII). A fragment of this cDNA coding for soluble IgE-binding factor fused with a fragment of human interleukin-3 gene was cloned in pBT-IL-3-sCD23 plasmid. It is demonstrated that E. coli strain JM109 (pBT-IL-3-sCD23) expresses the hybrid protein with a yield of 10-15% total cell protein. The recombinant product is represented by equal amounts of two polypeptides with molecular weights of about 24 and 32 kD. Immunological analysis and determination of the amino acid sequence of the N-terminal ends of these polypeptides show that a protein with a molecular weight of 24 kD results from proteolysis of the full-size (32 kD) hybrid protein. The preparation obtained can be used for the development of test kits for CD23.