FIG. 3. Interactions of transcription factors and RNA polymerase II with the human β-globin locus during early S-phase in synchronized K562 cells.

The cells were harvested at time 0 or at specific time points after release from cell cycle arrest (as indicated), and subjected to flow cytometry (shown on top) and ChIP using antibodies specific for RNA polymerase II (αpol II), the p45 subunit of NF-E2 (αNF-E2), and USF2 (αUSF2); time 0 represents the status of the blocked cells at the G₁/S-phase boundary. PCR was carried out using primers specific for HS2, the ∊-globin gene, the γ-globin gene, and the β-globin gene as indicated (see Fig. 1). The no antibody (no Ab) and input controls were processed as described in the legend to Fig. 2.