DETECTION OF AN IMMUNOGLOBULIN SWITCH REGION-SPECIFIC DNA-BINDING PROTEIN IN MITOGEN-STIMULATED MOUSE SPLENIC B-CELLS

We have detected a nuclear protein from lipopolysaccharide- and dextran sulfate-stimulated mouse splenic B cells which binds specifically to the immunoglobulin switch μ (Sμ) sequence. We have termed the binding protein NF-Sμ. DNA containing the Sμ repeated sequence, GAGCTGGGGTGAGCTGAGCTGAGCT, was used as a probe in electrophoretic mobility shift assays. Methylation interference analysis indicated that binding centers on the run of four guanine residues. Competitions with mutated Sμ sequences confirmed the importance of the run of G residues and revealed that optimal binding occurs when they are flanked by GAGCT. The kinetics of the expression of NF-Sμ in splenic B cells treated with lipopolysaccharide and dextran sulfate parallels the induction of recombinational activity at Sμ in these cells. On the basis of these data, we suggest that NF-Sμ may be an effector of switch recombination.