HDAC inhibition induces binding of acetylated histones H3 and H4 to the MLL transcriptional initiation site in primary MLL^PTD/WT leukemic blasts. (A) Primary MLL^PTD/WT AML blasts (UPN 300) and (B) primary MLL^WT/WT AML blasts (UPN 003) were cultured in media alone or in media containing 20 nM depsipeptide. An aliquot of cells was removed from each flask after 6 hours, and ChIP was performed with the indicated antibodies. PCR reactions with immunoprecipitated protein-DNA complexes were carried out using MLL- and GAPDH-specific primer pairs, and amplification products were detected in ethidium bromide–stained agarose gels for qualitative assessment. (C) Real-time PCR-based quantification of the ChIP with SybrGreen dye. Results are expressed as the percentage of change in modified histone levels at the MLL transcription initiation site in the depsipeptide-treated sample relative to media controls set to 100%.