About 5x107 pro-B cells were used for chromatin precipitation by streptavidin pulldown (Bio-ChIP) Ebert et al., 2011 The precipitated genomic DNA was quantified by real-time PCR, and at least 5 ng of ChIP-precipitated DNA were used as starting material for the generation of paired-end sequencing libraries as described by Illumina’s ChIP Sequencing sample preparation protocol followed by size selection of DNA fragments of 200–350 bp. Completed libraries were quantified with the Agilent Bioanalyzer dsDNA 1000 assay kit and Agilent QPCR NGS library quantification kit.