Patent ID: 8048645

Claim:
A method of producing a biologically active protein, which is a fragment of a biologically active primary translational product of an endogenous target gene, said protein being either the carboxy- or amino-terminal fragment of said primary translational product, wherein said protein is the extracellular binding domain of a membrane receptor or a proteolytic fragment of a structural extracellular matrix protein and has a biological activity which is distinct from the biological activity of said primary translational product, the method comprising: (i) culturing a host cell in which the target gene is endogenous, which host cell has been transfected with a DNA construct comprising: (a) a regulatory DNA segment which binds a regulatory polypeptide which can initiate or terminate transcription of the DNA encoding said protein and/or which is transcribed into a regulatory mRNA fragment capable of binding a regulatory polypeptide which can initiate or terminate translation of the mRNA encoding said protein, wherein said regulatory DNA segment allows the initiation of the transcription of the DNA encoding said protein and/or is transcribed into a regulatory mRNA fragment capable of binding a regulatory polypeptide which can initiate translation of the mRNA encoding said protein when said protein is the C-terminal fragment of said primary translational product, or wherein said regulatory DNA segment allows the termination of the transcription of the DNA encoding said protein and/or is transcribed into a regulatory mRNA fragment capable of binding a regulatory polypeptide which can terminate translation of the mRNA encoding said protein when said protein is the N-terminal fragment of said primary translational product; and (b) a DNA targeting segment comprising sequences homologous to a region of the target gene either 5′ or 3′ to the sequence coding for said protein, the construct being integrated within the host cell genomic DNA at a position determined by the DNA targeting segment such that expression of said protein is at least partially under control of the regulatory DNA segment; (ii) producing said protein from the transfected host cell; and (iii) collecting said produced protein.