BCL6 recruits MTA3 to a binding site located within intron 3 of the human PRDM1 locus. (A) Graphic representation of tiling ChIP on chip performed on the PRDM1 genomic locus in Ramos cells. The top portion of the graph shows fold enrichment of sequences within intron 3 by BCL6 (■) or actin (▩) antibodies versus input. The corresponding graphic representation of the PRDM1 locus (bottom) indicates the location of BCL6 binding, and the amplicon containing the BCL6 binding site that was used for QChIP in panels B-D. (B) QChIP was performed with BCL6, MTA3, and actin antibodies in Ramos cells for the site shown in panel A as well as a negative control promoter (CD20). The y-axis represents fold enrichment of the site relative to control (actin) antibody. Inset shows immunoblot of BCL6, MTA3, and actin in Ramos B-cell lymphoma cells. (C-D) Similar QChIP was performed in Ly1 DLBCL cells and in the BCL6⁻ Mutu III B-cell lymphoma cells, respectively. Error bars are SD.