Dynamic changes in RNA polymerase II occupancy during terminal maturation. (A) Western blot demonstrating levels of serine 2 phosphorylated (Ser2), serine 5 phosphorylated (Ser5), and total RNA polymerase II (Pol II) in day 4, day 7, and day 10 cells from the erythroid culture shown in Figure 1A. Histone H4 is used as a loading control. (B) Ser2 and Ser 5 Pol II occupancy at the α globin gene (i) and RPS19 (ii) gene in intermediate (day 7) and late (day 10) erythroblasts from the culture system shown in Figure 1A. (C) Heatmap depicting occupancy of Ser2 and Ser5 Pol II intermediate (Day 7) and late (Day 10) erythroblasts as determined by cut and tag. (D) Gene ontogeny analyses via GREAT of the top 1000 regions of Ser2 and Ser5 Pol II occupancy in intermediate (day 7) and late (day 10) erythroblasts. (E) Chromatin changes associated with loss of Ser2 Pol II occupancy during maturation. The heatmaps are ordered according to Ser2 Pol II occupancy in day 7 cells. (F) Changes in chromatin accessibility, Ser2 Pol II, Ser5 Pol II, H3K36me3 and H3K27me3 occupancy at the MYC locus during erythroid maturation.