Expression of a biologically active fragment of human IgE ε chain in Escherichia coli

cDNA corresponding to human IgE heavy (ε) chain mRNA was cloned from human IgE-secreting myeloma U255 cells. Partial nucleotide sequence analysis demonstrated that the cloned cDNA contained the coding region for about two-thirds of the C(H)2 and all of the C(H)3 and C(H)4 domains as well as the 3'-untranslated region. This ε DNA was inserted into expression vector pUC7 and expression of an ε-chain fragment in Escherichia coli was demonstrated by protein blot analysis using ¹²⁵I-labeled anti-human IgE as probe. The expression product was purified on a column of goat anti-human IgE-conjugated Sepharose 4B and the polypeptide was found to retain binding activity to human basophils.