Immunoglobulin gene promoters are active only in lymphoid cells and this tissue-specific activity requires an octamer sequence, ATTTGCAT (refs 1-9). Paradoxically, this same octamer motif seems to be a transcriptional control element in promoters which are active in all tissues10. Using an electrophoretic mobility shift assay to identify DNA binding proteins, we have now detected two species of nuclear proteins which bind specifically to this octamer. One previously characterized form11 (NF-Al) was found in all cell lines tested while the other form (NF-A2) was restricted to lymphoid cell lines. NF-A2 was found in cell lines representing all stages of B-cell differentiation and in half of the T-lymphoma cell lines tested. The identification of a lymphoid-specific octamer binding protein may account for the lymphoid-specific activity of immunoglobulin promoters.
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