Binding of Pax-5 and spliced variant Pax-5/Δ-Ex8 to the AID promoter. (A) EMSA of nuclear extracts of CLL B cells from 2 patients was performed. The asterisk indicates a nonspecific band. Oligoprobes containing the P3 promoter region of the AID gene without nuclear extracts was used as control. (B) Western blot analysis with anti–Pax-5 (C-20) goat polyclonal IgG was performed to assess the specificity of the complex detected in EMSA. Solid lines (bands a and b) indicate the Pax-5a– and Pax-5/Δ-Ex8–containing complexes, respectively, in both assays (EMSA and Western blot). One of 3 independent experiments is shown.