PAX5 (BSAP) REGULATES THE MURINE IMMUNOGLOBULIN 3'ALPHA ENHANCER BY SUPPRESSING BINDING OF NF-ALPHA-P, A PROTEIN THAT CONTROLS HEAVY-CHAIN TRANSCRIPTION

The Pad transcription factor BSAP (B-cell-specific activator protein) is known to bind to and repress the activity of the immunoglobulin heavy chain 3'alpha enhancer, We have detected an element-designated alpha P-that lies approximate to 50 bp downstream of the BSAP binding site 1 and is required for maximal enhancer activity, In vitro binding experiments suggest that the 40-kDa protein that binds to this element (NF-alpha P) is a member of the Ets family present in both B-cell and plasma-cell nuclei. However, in Five footprint analysis suggests that the alpha P site is occupied only in plasma cells, whereas the BSAP site is occupied in B cells but not in plasma cells. When Pax5 binding to the enhancer in B cells Has blocked in vivo by transfection with a triple-helix-forming oligonucleotide, an alpha P footprint appeared and endogenous immunoglobulin heavy chain transcripts increased, The tripie-helix-forming oligonucleotide also increased enhancer activity of a transfected construct in B cells, but only when the alpha P Site was intact. Pax5 thus regulates the 3'alpha enhancer and immunoglobulin gene transcription by blocking activation by NF-alpha P.