Active Motif Epigenetic Services performed ChIP assays. Cells fixed with 1% formaldehyde for 15 min were quenched with 0.125 M lysine, and then swollen in lysis buffer for 30 min on ice. Chromatin was isolated after sonication to shear the DNA to an average length of 300-500 bp. ChIP and input DNAs were prepared for amplification by converting overhangs into phosphorylated blunt ends and adding an adenine to the 3' ends. Illumina adaptors were added and the library was size-selected (175-225 bp) on an agarose gel. The adaptor- ligated libraries were amplified for 18 cycles. The resulting DNA libraries were purified, quantified, and tested by qPCR at the same specific genomic regions as the original ChIP DNA to assess quality of the amplification reactions.