not-yet-known not-yet-known not-yet-known unknown ChIP-Seq and data analysis Chromatin Immuno Precipitation (ChIP) was performed as previously described 55, with minor modifications. Per ChIP, 100K crosslinked mature primary human mast cells were used. Sonicated chromatin was immunoprecipitated using 1 μg of anti-H3K27Ac antibody (Abcam, Ab4729), 1 μg of anti-H3K4Me2 antibody (Abcam, Ab32356) and 25 μl BSA-blocked Protein A agarose beads (Millipore #16-125). Illumina sequencing libraries were prepared using the ThruPLEX DNA-Seq Kit (Rubicon Genomics) and sequenced on an Illumina HiSeq2500 sequencer (single read 50 bp length, 17-21 million reads per sample). Reads were aligned to the human GRCh38 genome build using HISAT2 56 with standard parameters and parsed to HOMER 53 for downstream analyses. Tag directories were generated for each sample with removal of duplicate reads (-tbp 1 option). BedGraph files displaying normalized counts (reads per million) were generated for direct visualization in the UCSC Genome Browser using the makeUCSCfile HOMER script. H3K27Ac enriched regions were identified using HOMER findPeaks with -region -size 150 -minDist 370 (parameter set 1) or -region -size 1000 -minDist 2500 (parameter set 2) options. Histograms of ChIP signals were generated with the annotatePeaks script (using the -hist option). ChIP-Seq datasets were deposited in the Gene Expression Omnibus (GEO), accession number pending. Differential peaks were calculated using DESeq2 using default settings (fold change > 2 and adjusted P value < 0.05). Intersect peak files of two different peak files were analyzed via the Genomic Regions Enrichment of Annotations Tool (GREAT), to obtain the distance to associated TSS data. Genomic locations of (differentially) acetylated regions were annotated using the ROSE algorithm and HOMER.