library_construction_protocol: Cells were fixed in 1% formaldehyde for 12 minutes, swelled in 0.5% SDS buffer then lysed in 0.5% SDS + 5% Triton buffer (2:1). Genomic DNA was sheared to 100-500bp by sonication. ChIP libraries were prepared using NEBNext Ultra II DNA Library Prep Kit for Illumina (NEB).