The Flag-bio tagged mouse ES cells were fixed in 1% formaldehyde for 7 minutes at room temperature. The formaldehyde was quenched using 2.5M glycine before harvest for extract preparation. Whole cell extracts were sonicated to solubilize the chromatin. The chromatin extracts containing DNA fragments with size of 500-800bp were immunoprecipitated using Streptavidin beads (Dynabeads MyOne Streptavidin T1), and 2% SDS was applied for one of the washing steps. massive parallel sequencing (bioChIP-Seq)