P19 embryonal carcinoma cells were cultured in DMEM with 10% fetal calf serum, The mouse P19ECs were obtained from ATCC and were cultured in DMEM, 10% fetal 655 calf serum, 2mM L-glutamine (Gibco) and 50 ug/ml penicillin/streptomycin (Gibco) P19ECs were co-transfected with TRE-Tight BLIMP1-EGFP, and and pCAG-tTA-IP using Lipofectamine 2000 (Invitrogen) according to the manufacturer's instructions. The cells were harvested and crosslinked with 1% formaldehyde 24 hours after transfection. Phenol Chloroform extraction Performed ChIP according to: Magnusdottir, E. et al. Epidermal terminal differentiation depends on B lymphocyte912 induced maturation protein-1. Proceedings of the National Academy of Sciences of the United States of America 104, 14988-93 (2007). Libraries were generated using Illumina ChIPseq DNA Sample 665 Preparation Kit, (cat. No 1003473)