ChIP-seq: Cells were cross-linked by a two-step procedure, with 2mM disuccinimidyl glutarate for 30 minutes at room temperature and then with 1% formaldehyde for 10 min at 37°C. The ChIP lysis buffer composition was 50mM Tris-HCl pH 8, 10mM EDTA, 1% SDS and 1X Protease Inhibitor Cocktail w/o EDTA. After lysis, chromatin extract were sonicated to reduce the length of DNA fragments to 200-400 bp using a Diagenode Bioruptor. ChIP-seq library: ChIP-seq libraries were prepared according to Illumina's instructions accompanying the DNA Sample Kit. Sequencing was performed on Illumina Genome Analyzer IIx (IGBMC) single-end 36bp.