Trans-acting factors that mediate B-cell specific transcription of immunoglobulin genes have been postulated based on an analysis of the expression of exogenously introduced immunoglobulin gene recombinants in lymphoid and non-lymphoid cells. Two B-cell-specific, cis-acting transcriptional regulatory elements have been identified. One element is located in the intron between the variable (V) and constant (C) regions of both heavy and κ light-chain genes and acts as a transcriptional enhancer1-6. The second element is found upstream of both heavy and κ light-chain gene promoters. This element directs lymphoid-specific transcription even in the presence of viral enhancers7-10. We have sought nuclear factors that might bind specifically to these two regulatory elements by application of a modified gel electrophoresis DNA binding assay11-13. We report here the identification of a human B-cell nuclear factor (IgNF-A) that binds to DNA sequences in the upstream regions of both the mouse heavy and κ light-chain gene promoters and also to the mouse heavy-chain gene enhancer. This sequence-specific binding is probably mediated by a highly conserved sequence motif, ATTTGCAT, present in all three transcriptional elements. Interestingly, a factor showing similar binding specificity to IgNF-A is also present in human HeLa cells.
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