BCL6 binds to its exon 1 sequence in vivo (ChIP assay), and the binding is abrogated by BCL6 deregulating mutations.

(A) Schematic representation of the human BCL6 locus; the 4 genomic fragments amplified for analysis are approximately positioned below the map (B1 and B2, test region; A and D, control regions). (B) Ethidium bromide–stained agarose gels of PCR products A to D obtained from 2 BCL6-expressing cell lines (Ly1 and P3HR1) and a control line that lacks BCL6 expression (CB33). After formaldehyde cross-linking, chromatin was immunoprecipitated using the anti-BCL6 antibody N3 or an irrelevant antibody (IgG) as control, and PCR reactions were performed on ChIP products, total chromatin before immunoprecipitation (input), and genomic DNA as a positive control for PCR. One sample was also processed with no antibody to serve as a negative control. (C) BCL6 binds to the wild-type allele but not to the mutated allele in the Ly1 cell line. Direct sequencing of PCR products obtained from genomic DNA, total input, and immunoprecipitated chromatin (ChIP) in the Ly1 cell line and in P3HR1 as a control. Arrows indicate the position of the mutations (Ly1, 257T>C; P3HR1, 380T>A and 397T>G).