Figure 9.
RNA PolII is only detectable at the α-globin promoters late in differentiation. ChIP assay shows no enrichment of PolII in cells not expressing α globin. By contrast, the β-actin promoter (B) binds PolII in these cells, decreasing later in erythroid differentiation as the nucleus becomes pyknotic and expression of many genes (but not globin) is diminished. In globin-expressing cells (I. MEL and Ter119-selected cells), PolII binds not only the α-globin promoters but also β-HS2 as previously described (Johnson et al, 2002) (A). Simultaneously, very small enrichment of PolII can be detected upstream the α genes.