Transcription factor assembly at the Cd19 enhancer. (A) In vivo DMS footprinting assays were performed using primary cells. DMS-modified DNA was amplified using LM-PCR with primers specific for the upper strand of the enhancer region. G indicates in vitro DMS treated DNA; MEF, mouse embryonic fibroblast; thy-T, Thy1⁺ thymocytes; BM-B, CD19⁺ bone marrow cells; Sp-B, CD19⁺ splenocytes. Vertical lines on the right indicate transcription factor binding sites identified by sequence analysis. Symbols are as in Figure 2. (B) Sequence alignment with consensus binding sites. DNA sequence at the enhancer was aligned with consensus sequence of transcription factor binding sites (E47, EBF, RUNX1, ETS, PAX5). Symbols are as in Figure 2. (C) ChIP experiments performed on Thy1⁺ thymocytes (T) and CD19⁺ splenocytes (B) using antibodies against PAX5, E2A, and EBF. Enrichment was measured at the enhancer and a control region at +10 kb. Relative enrichment was normalized against 45S rRna promoter.