Polypeptide competitor for immunoglobulin E

A polypeptide which is capable of binding specifically to the high affinity Fc receptor sites for IgE which exists on human cells and which has the following amino acid sequence:

• X-Gln-Lys-His-Trp-Leu-Ser-Asp-Arg-Thr-Tyr-
• Thr-Cys-Gln-Val-Thr-Tyr-Gln-Gly-His-Thr-
• Phe-Glu-Asp-Ser-Thr-Lys-Lys-Cys-Ala-Asp-
• Ser-Asn-Pro-Arg-Gly-Val-Ser-Ala-Tyr-Leu-
• Ser-Arg-Pro-Ser-Pro-Phe-Asp-Leu-Phe-Ile-
• Arg-Lys-Ser-Pro-Thr-Ile-Thr-Cys-Leu-Val-
• Val-Asp-Leu-Ala-Pro-Ser-Lys-Gly-Thr-Val-
• Asn-Leu-Thr-Trp-Ser-Arg- Y,
• in which X and Y are oligopeptide sequences initiating and terminating the chain which do not prevent said polypeptide from binding specifically to the high affinity Fc receptor sites on human cells and are not physiologically harmful.

A method of preparing the polypeptide, said method comprising the steps of:

• culturing a host transformed by a vector comprising a DNA segment having the following nucleotide sequence:
• CAG AAG CAC TGG CTG TCA GAC CGC ACC TAC
• ACC TGC CAG GTC ACC TAT CAA GGT CAC ACC
• TTT GAG GAC AGC ACC AAG AAG TGT GCA GAT
• TCC AAC CCG AGA GGG GTC AGC GCC TAC CTA
• AGC CGG CCC AGC CCG TTC GAC CTG TTC ATC
• CGC AAG TCG CCC ACG ATC ACC TGT CTG GTC
• GTC GAC CTG GCA CCC ACC AAG GGG ACC GTG
• AAC CTG ACC TGG TCC CGG
• isolating the polypeptide from the culture to obtain a polypeptide as claimed in claim 17;
• and
• treating that polypeptide to remove the chain initiating and terminating groups X and Y.