Samples were divided into 200μl aliquots, prewarmed to 25°C and incubated with MNase (stored in MNase storage buffer (10mM Hepes pH7.5/100mM NaCl/1mM CaCl2/50% glycerol) and diluted in MNase dilution buffer (50mM Tris-HCl pH8/10mM NaCl/126mM CaCl2/5% glycerol)). Concentration of MNase and time of incubation were optimized to obtain 80% mononucleosomes as determined by BioAnalyzer analysis. Libraries were prepared using the Illumina sequencing library preparation protocol.