<b>DELETION OF IMMUNOGLOBULIN HEAVY CHAIN GENES ACCOMPANIES THE CLASS SWITCH </b><b>REARRANGEMENT </b>

TL;DRAbstract

The organization of immunoglobulin heavy chain genes has been investigated by Southern blot hybridization of restriction DNA fragments using cloned Tl, 7'2b and /1 genes as probes. The organization of the heavy chain genes (/1, 7'1, T2b and 72a) was compared in newborn mouse (BALB/c) and myelomas producing IgM, IgG3, IgGl, IgG2b, IgG2a and IgA. The 7'1 gene was present in DNAs from IgM-,IgG3-and IgGl-producing myelomas but absent in DNAs from IgG2b-, IgG2a-and lgA-producing myelomas. The r2b gene was found in DNAs from IgM-, IgG3, IgGl-and IgG2b-producing myelomas but deleted in DNAs from IgG2a-and IgA-producing myelomas. The 72a gene was present in DNAs from all the myelomas tested except IgA-producing myelomas. The /1 gene was present in DNAs from IgM-and IgG2b-producing myelomas but absent in DNAs from IgG3-, IgGl-, IgG2a and IgA-producing myelomas. The heavy chain genes expressed in most myelomas were rearranged in different forms on different homologous chromosomes. In some myelom

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