Hemin induction of K562-EBNA1 cells episomally transfected with EBACs carrying EGFP modifications in the β-globin locus.

Pools of transfected cells were grown continuously in the presence of hygromycin for 40 days before flow cytometry (shaded, no hemin induction). Transfected cells were induced for 5 days with hemin. (A) Comparison of EGFP expression without (shaded) and with hemin (100μM) induction (unshaded) in the various EGFP constructs, as indicated. The percent of cells expressing EGFP and the median peak fluorescence (MPF) without and with hemin is shown for each construct. (B) The effect of hemin induction on EGFP gene expression was determined by measuring MPF on day 3 (filled symbols) and day 5 (empty symbols) at different hemin doses, for the same constructs as in panel A. The data represent the means ± SD of 3 independent experiments.