Analysis of combinatorial binding identifies the heptad as the prevalent pattern in human CD34⁺HSPCs. (A) The number of peaks for combinations of 2, 5, 6, and all 7 TFs is shown on the left of the figure (red = bound; blue = unbound). A complete set of all 119 combinations involving binding of 2 or more factors is shown in supplemental Table 2. Z scores on the right indicate significance of deviation between observed and expected events for the corresponding patterns. (B) Raw ChIP-seq reads for each transcription factor, control IgG, and H3K27ac are displayed as density plots in the University of California Santa Cruz (UCSC) genome browser above tracks for gene structure and expression in hCD34. The black vertical bar (in the Peak Calls row) above the density plots corresponds to peak coordinates at HHEX +1, a previously verified hematopoietic enhancer that was also bound by the heptad in mouse HPC7 cells. (C) De novo motif discovery performed on the set of regions bound by all 7 TFs identifies ETS, GATA, E-box, and RUNX motifs, corresponding to the 4 motifs that would be expected for these factors as those most significantly enriched.