Analysis of histone H3 and H4 modifications in the transgene cassette. ChIP analysis of acetylated histone H3 (H3Ac) (A), histone H3 with trimethylated lysine 9 (H3K9me3) (B), H3K4me2 (C), H3K27me3 (D), and H4K20me3 (E) in RL4 cells carrying the indicated constructs with or without zebularine treatment. The primers and probes used included mAmy (murine amylase), GFP (the EGFP gene), AG (the AG region of Rep-P), mBG (a murine β-globin sequence), and hBG (human β-globin promoter). GFP, AG, and hBG are sequences from the transgene. Zeb GFP +, cells treated for 1 to 2 weeks with zebularine and exhibiting expression of the EGFP marker; Zeb GFP −, cells treated for 4 to 5 weeks with zebularine and exhibiting resilencing. The results of 1 representative experiment of 3 experiments are shown.