Chromatin was enzymatically sheared into fragments with an average size of 300-500 bp using the ChIP-IT Express Enzymatic Kit (Active Motif). Sequencing libraries were prepared from ChIP DNA according to the Illumina protocols. Briefly, ChP DNA was end-repaired, A-tailed, ligated to the adapters, size selected to 200-400 bp and amplified by 18 cycles of PCR. Libraries were sequenced on the Genome Analyzer Iix (Illumina) as single-end 50-bp reads.