Location of the genes for human heavy chain immunoglobulin to chromosome 6

Immunoglobulin synthesis was examined in 31 man-mouse hybrid clones produced by fusing RAG mouse cells with human lymphoid cells. Cells were grown in serum-free medium containing [¹⁴C]leucine and a¹⁴C-labeled. amino acid mixture. Spent medium was dialyzed, concentrated, and subjected to radioimmunoelectrophoresis. Eighteen clones were found to produce material that gave a radiolabeled precipitin line with anti-human IgG (γ-chain specific). Production of material which was indistinguishable on radioimmunoelectrophoresis from human Ig γ heavy chain, was dependent on the presence in hybrid clones of human chromosome 6. The material was found to have the ion-exchange elution characteristics of human IgG. When radiolabeled spent medium from human lymphoid lines and from chromosome 6-positive hybrid clones was exposed to protein A-Sepharose and bound material eluted with 8 M urea was subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis, three radiolabeled peaks occurred with molecular weights of approximately 55,000 (coinciding with that of Ig γ heavy chain), 40,000, and 25,000 (coinciding with that of Ig light chains). No similar peaks were detected in experiments where spent medium from RAG cells was treated identically. These studies lead us to conclude that certain RAG-human lymphoid hybrid clones produce human IgG and that the structural genes for γ heavy chains are located on human chromosome 6. These results also imply that the locus coding for human α,-antitrypsin (Pi) is located on chromosome 6.