We next assessed how the observed changes in histone acetylation upon butyrate treatment translate into altered gene expression. We observed hypo-acetylated TSS peaks near several downregulated genes, including the mast cell activation-associated genes BTK (3.97 fold decrease expression), SYK (3.89 fold), MRGPRX2 (4.86 fold) and KIT (2.45 fold) (Fig. 4A). Overall acetylation at the TSS of the 864 (Fig. 1B) downregulated genes was strongly and immediately reduced upon butyrate exposure (Fig. 4B, left histogram). Although TSS acetylation was also reduced at transcriptionally unchanged genes (defined as the 600 genes with the lowest fold chance in expression after butyrate treatment) and the 551 upregulated genes (Fig. 4B, middle and right histogram), the quantitative reduction in area under the curve was strongest and fastest for the 864 downregulated genes (Fig. 4C).