| Abstract
| - The murine Ig heavy chain gene locus is regulated by multiple elements. In addition to the intron enhancer, Eμ, there is a complex regulatory region 3' of the Cα gene, which spans ∼40 kb and contains several enhancers. In contrast to mouse, the human IgH cluster contains two Calpha; genes, each associated with duplicated arrays of other CH genes. There is evidence to suggest that each array is individually regulated. In this report, we describe an ∼2 kb region containing 20 bp repeats that lies 3' of both human Cα1 and Cα2 genes. This repeat region appears to be the site of integration of the Epstein-Barr virus in the RGN1 B lymphoma cell line. The repeat region is homologous to a 420 bp segment in mouse that is located downstream of the Cα membrane exon in the interval preceding the second of three poly(A) termination sites. However, in contrast to human, the murine segment contains degenerate repeats. The human repeat region bears significant homology to switch sequences, in particular to Sμ and Sα. We hypothesize that the human repeat regions may play a role in the class switch process by contributing to the stabilization of interactions between the two switch regions. The presence of a SauβA site within the repeats presents a barrier to cloning with several existing human genomic libraries, most of which are based on partial Sau3A digestion. Furthermore, the homology of the repeat region with Sμand Sα sequences may contribute to the difficulty in isolating YAC clones containing Cα genes since homologous recombination could potentially have deleted this entire segment. Our map of these DNA segments provides a guide to their isolation and characterization.
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