Briefly, cells were grown to log phase and fixed with 1% formaldehyde for 10 min at room temperature. The fixed cells were sonicated directly. Exactly 10% of the chromatin was used for the extraction of input DNA. For ChIP, 4 μg of antibodies, including anti-H3K4me3 or anti-H3K27me3 antibodies, was bound to protein A or protein G magnetic beads depending on the antibody origin. The ChIP-Seq libraries were constructed using the TruSeq DNA sample prep kit v2 (Illumina) according to the manufacturer's protocol.