(A) A Venn diagram showing the overlap between CDK8 peaks (n = 24273) and NMIs (n = 27698). (B) A scatter plot showing Spearman correlation between CDK8 signal and BioCAP at NMIs. (C) Heatmaps showing enrichment of CDK8, FS2-FBXL19 and BioCAP at FBXL19 peaks (n = 11322) sorted by decreasing FBXL19 signal. (D) A Venn diagram showing the overlap between FBXL19 peaks (n = 11322), CDK8 peaks (n = 24273), and NMIs (n = 27698). Percent overlap of all FBXL19 peaks is shown. (E) A schematic of the Fbxl19fl/fl allele showing the location of the loxP sites. Treatment with tamoxifen (OHT) results in Cre-mediated deletion of the second exon, encoding for the ZF-CxxC domain but leaving the rest of the gene and protein intact. (F) RT-qPCR of FBXL19 expression in Fbxl19fl/fl ES cells before (WT) and following tamoxifen treatment (OHT). Primers specific for the ZF-CxxC and LRR domains were used. Expression is relative to expression in WT ES cells. Error bars show SEM of three biological experiments. (G) A Western blot analysis of the expression of Mediator subunits in Fbxl19fl/fl (WT) and Fbxl19ΔCXXC (OHT) ES cells. HDAC1 and TBP were probed as loading controls. (H) Heatmaps showing enrichment of CDK8 in Fbxl19fl/fl (WT) and Fbxl19ΔCXXC (OHT), FS2-FBXL19 and BioCAP signal at ATAC peaks divided based on change in CDK8 binding in Fbxl19ΔCXXC ES cells as in Figure 4E. The mean of the enrichment for each group is shown above the heatmaps. Left: zoomed heatmaps for ATAC peaks associated with a decrease (↓) or an increase (↑) in CDK8 binding and a differential heatmap representing log2 fold change of CDK8 signal between OHT and WT samples at the differential peaks. (I) Percent overlap between CDK8 peaks (as in Figure 4E) and transcription start sites of genes (TSS, left) or FBXL19 peaks (right). (J) Metaplots showing enrichment of FS2-FBXL19, BioCAP and CDK8 ChIPseq signal at all CDK8 peaks (left), FBXL19-bound CDK8 peaks (FBXL19+, middle) and nonFBXL19 CDK8 peaks (FBXL19-, right). Peaks were divided based on change in CDK8 binding in Fbxl19ΔCXXC ES cells as in Figure 4E.