A lymphoid-specific protein binding to the octamer motif of immunoglobulin genes

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.